Lex and Yacc: a Brisk Tutorial
Total Page:16
File Type:pdf, Size:1020Kb
Load more
Recommended publications
-
Wait, I Don't Want to Be the Linux Administrator for SAS VA
SESUG Paper 88-2017 Wait, I don’t want to be the Linux Administrator for SAS VA Jonathan Boase; Zencos Consulting ABSTRACT Whether you are a new SAS administrator or switching to a Linux environment, you have a complex mission. This job becomes even more formidable when you are working with a system like SAS Visual Analytics that requires multiple users loading data daily. Eventually a user will have data issues or create a disruption that causes the system to malfunction. When that happens, what do you do next? In this paper, we will go through the basics of a SAS Visual Analytics Linux environment and how to troubleshoot the system when issues arise. INTRODUCTION Many companies choose to implement SAS Visual Analytics in a Linux environment. With a distributed deployment, it’s the only choice but many chose this operating system because it reduces operating costs. If you are the newly chosen SAS platform administrator, you might be more versed in a Windows environment and feel intimidated by Linux. This paper introduces using basic Linux commands and methods for troubleshooting a SAS Visual Analytics environment. The paper assumes that SAS Visual Analytics is installed on a SAS 9.4 platform for Linux and that the reader has some familiarity with other operating systems, such as Windows. PLATFORM ADMINISTRATION 101 SAS platform administrators work with three main product areas. Each area provides a different functionality based on the task the administrator needs to perform. The following figure defines each area and provides a general overview of its purpose. Figure 1 Platform Administrator Tools Operating System SAS Management SAS Environment •Contains installed Console Manager software •Access and manage the •Monitor the •Contains logs used for metadata environment troubleshooting •Control database •Configure custom alerts •Administer host system connections users •Manage user accounts •Manage the LASR server With any operating system, there is always a lot to learn. -
Windows Command Prompt Cheatsheet
Windows Command Prompt Cheatsheet - Command line interface (as opposed to a GUI - graphical user interface) - Used to execute programs - Commands are small programs that do something useful - There are many commands already included with Windows, but we will use a few. - A filepath is where you are in the filesystem • C: is the C drive • C:\user\Documents is the Documents folder • C:\user\Documents\hello.c is a file in the Documents folder Command What it Does Usage dir Displays a list of a folder’s files dir (shows current folder) and subfolders dir myfolder cd Displays the name of the current cd filepath chdir directory or changes the current chdir filepath folder. cd .. (goes one directory up) md Creates a folder (directory) md folder-name mkdir mkdir folder-name rm Deletes a folder (directory) rm folder-name rmdir rmdir folder-name rm /s folder-name rmdir /s folder-name Note: if the folder isn’t empty, you must add the /s. copy Copies a file from one location to copy filepath-from filepath-to another move Moves file from one folder to move folder1\file.txt folder2\ another ren Changes the name of a file ren file1 file2 rename del Deletes one or more files del filename exit Exits batch script or current exit command control echo Used to display a message or to echo message turn off/on messages in batch scripts type Displays contents of a text file type myfile.txt fc Compares two files and displays fc file1 file2 the difference between them cls Clears the screen cls help Provides more details about help (lists all commands) DOS/Command Prompt help command commands Source: https://technet.microsoft.com/en-us/library/cc754340.aspx. -
Drilling Network Stacks with Packetdrill
Drilling Network Stacks with packetdrill NEAL CARDWELL AND BARATH RAGHAVAN Neal Cardwell received an M.S. esting and troubleshooting network protocols and stacks can be in Computer Science from the painstaking. To ease this process, our team built packetdrill, a tool University of Washington, with that lets you write precise scripts to test entire network stacks, from research focused on TCP and T the system call layer down to the NIC hardware. packetdrill scripts use a Web performance. He joined familiar syntax and run in seconds, making them easy to use during develop- Google in 2002. Since then he has worked on networking software for google.com, the ment, debugging, and regression testing, and for learning and investigation. Googlebot web crawler, the network stack in Have you ever had the experience of staring at a long network trace, trying to figure out what the Linux kernel, and TCP performance and on earth went wrong? When a network protocol is not working right, how might you find the testing. [email protected] problem and fix it? Although tools like tcpdump allow us to peek under the hood, and tools like netperf help measure networks end-to-end, reproducing behavior is still hard, and know- Barath Raghavan received a ing when an issue has been fixed is even harder. Ph.D. in Computer Science from UC San Diego and a B.S. from These are the exact problems that our team used to encounter on a regular basis during UC Berkeley. He joined Google kernel network stack development. Here we describe packetdrill, which we built to enable in 2012 and was previously a scriptable network stack testing. -
Your Performance Task Summary Explanation
Lab Report: 11.2.5 Manage Files Your Performance Your Score: 0 of 3 (0%) Pass Status: Not Passed Elapsed Time: 6 seconds Required Score: 100% Task Summary Actions you were required to perform: In Compress the D:\Graphics folderHide Details Set the Compressed attribute Apply the changes to all folders and files In Hide the D:\Finances folder In Set Read-only on filesHide Details Set read-only on 2017report.xlsx Set read-only on 2018report.xlsx Do not set read-only for the 2019report.xlsx file Explanation In this lab, your task is to complete the following: Compress the D:\Graphics folder and all of its contents. Hide the D:\Finances folder. Make the following files Read-only: D:\Finances\2017report.xlsx D:\Finances\2018report.xlsx Complete this lab as follows: 1. Compress a folder as follows: a. From the taskbar, open File Explorer. b. Maximize the window for easier viewing. c. In the left pane, expand This PC. d. Select Data (D:). e. Right-click Graphics and select Properties. f. On the General tab, select Advanced. g. Select Compress contents to save disk space. h. Click OK. i. Click OK. j. Make sure Apply changes to this folder, subfolders and files is selected. k. Click OK. 2. Hide a folder as follows: a. Right-click Finances and select Properties. b. Select Hidden. c. Click OK. 3. Set files to Read-only as follows: a. Double-click Finances to view its contents. b. Right-click 2017report.xlsx and select Properties. c. Select Read-only. d. Click OK. e. -
Chapter # 9 LEX and YACC
Chapter # 9 LEX and YACC Dr. Shaukat Ali Department of Computer Science University of Peshawar Lex and Yacc Lex and yacc are a matched pair of tools. Lex breaks down files into sets of "tokens," roughly analogous to words. Yacc takes sets of tokens and assembles them into higher-level constructs, analogous to sentences. Lex's output is mostly designed to be fed into some kind of parser. Yacc is designed to work with the output of Lex. 2 Lex and Yacc Lex and yacc are tools for building programs. Their output is itself code – Which needs to be fed into a compiler – May be additional user code is added to use the code generated by lex and yacc 3 Lex : A lexical analyzer generator Lex is a program designed to generate scanners, also known as tokenizers, which recognize lexical patterns in text Lex is an acronym that stands for "lexical analyzer generator.“ The main purpose is to facilitate lexical analysis The processing of character sequences in source code to produce tokens for use as input to other programs such as parsers Another tool for lexical analyzer generation is Flex 4 Lex : A lexical analyzer generator lex.lex is an a input file written in a language which describes the generation of lexical analyzer. The lex compiler transforms lex.l to a C program known as lex.yy.c. lex.yy.c is compiled by the C compiler to a file called a.out. The output of C compiler is the working lexical analyzer which takes stream of input characters and produces a stream of tokens. -
Text Editing in UNIX: an Introduction to Vi and Editing
Text Editing in UNIX A short introduction to vi, pico, and gedit Copyright 20062009 Stewart Weiss About UNIX editors There are two types of text editors in UNIX: those that run in terminal windows, called text mode editors, and those that are graphical, with menus and mouse pointers. The latter require a windowing system, usually X Windows, to run. If you are remotely logged into UNIX, say through SSH, then you should use a text mode editor. It is possible to use a graphical editor, but it will be much slower to use. I will explain more about that later. 2 CSci 132 Practical UNIX with Perl Text mode editors The three text mode editors of choice in UNIX are vi, emacs, and pico (really nano, to be explained later.) vi is the original editor; it is very fast, easy to use, and available on virtually every UNIX system. The vi commands are the same as those of the sed filter as well as several other common UNIX tools. emacs is a very powerful editor, but it takes more effort to learn how to use it. pico is the easiest editor to learn, and the least powerful. pico was part of the Pine email client; nano is a clone of pico. 3 CSci 132 Practical UNIX with Perl What these slides contain These slides concentrate on vi because it is very fast and always available. Although the set of commands is very cryptic, by learning a small subset of the commands, you can edit text very quickly. What follows is an outline of the basic concepts that define vi. -
Shells and Shell Scripting
Shells and Shell scripting What is a Shell? • A shell is a command line interpreter that is the interface between the user and the OS. • A “program launcher” of sorts. • The shell: o analyzes each command o determines what actions are to be performed o performs the actions • Example: wc –l file1 > file2 Which shell? • sh – Bourne shell o Most common, other shells are a superset o Good for programming • csh or tcsh – default for command line on CDF o C-like syntax o Best for interactive use. Not good for programming. • bash – default on Linux (Bourne again shell) o Based on sh, with some csh features. • korn – written by David Korn o Based on sh – Some claim best for programming. o Commercial product. Common shell facilities Shell startup When a shell is invoked, it does the following: 1. Read a special startup file (usually in home directory) 2. display prompt and wait for command 3. Ctrl-D on its own line terminates shell, otherwise, goto step 2. Shell startup files used to set shell options, set up environment variables, alias sh – executes .profile if it’s there. ksh – executes .profile if in interactive mode. Executes $ENV (usually $HOME/.kshrc) csh – executes .cshrc if it exists. If a login shell, executes .login bash – executes .bashrc, if a login shell, executes .bash_profile instead Executables vs. built-in commands Most commands you run are other compiled programs. Found in /bin Example: ls – shell locates ls binary in /bin directory and launches it Some are not compiled programs, but built into the shell: cd, echo Input-output redirection prog < infile > outfile ls > outfile 2>&1 # sh stdout and stderr Pipelining commands send the output from one command to the input of the next: ls -l | wc ps –aux | grep reid | sort Before a program is executed, the shell recognizes the special characters such as <, >, |, and rewires the standard input, output, or error file descriptors of the program about to be executed to point to the right files (or the standard input of another program). -
Project1: Build a Small Scanner/Parser
Project1: Build A Small Scanner/Parser Introducing Lex, Yacc, and POET cs5363 1 Project1: Building A Scanner/Parser Parse a subset of the C language Support two types of atomic values: int float Support one type of compound values: arrays Support a basic set of language concepts Variable declarations (int, float, and array variables) Expressions (arithmetic and boolean operations) Statements (assignments, conditionals, and loops) You can choose a different but equivalent language Need to make your own test cases Options of implementation (links available at class web site) Manual in C/C++/Java (or whatever other lang.) Lex and Yacc (together with C/C++) POET: a scripting compiler writing language Or any other approach you choose --- must document how to download/use any tools involved cs5363 2 This is just starting… There will be two other sub-projects Type checking Check the types of expressions in the input program Optimization/analysis/translation Do something with the input code, output the result The starting project is important because it determines which language you can use for the other projects Lex+Yacc ===> can work only with C/C++ POET ==> work with POET Manual ==> stick to whatever language you pick This class: introduce Lex/Yacc/POET to you cs5363 3 Using Lex to build scanners lex.yy.c MyLex.l lex/flex lex.yy.c a.out gcc/cc Input stream a.out tokens Write a lex specification Save it in a file (MyLex.l) Compile the lex specification file by invoking lex/flex lex MyLex.l A lex.yy.c file is generated -
User Manual for Ox: an Attribute-Grammar Compiling System Based on Yacc, Lex, and C Kurt M
Computer Science Technical Reports Computer Science 12-1992 User Manual for Ox: An Attribute-Grammar Compiling System based on Yacc, Lex, and C Kurt M. Bischoff Iowa State University Follow this and additional works at: http://lib.dr.iastate.edu/cs_techreports Part of the Programming Languages and Compilers Commons Recommended Citation Bischoff, Kurt M., "User Manual for Ox: An Attribute-Grammar Compiling System based on Yacc, Lex, and C" (1992). Computer Science Technical Reports. 21. http://lib.dr.iastate.edu/cs_techreports/21 This Article is brought to you for free and open access by the Computer Science at Iowa State University Digital Repository. It has been accepted for inclusion in Computer Science Technical Reports by an authorized administrator of Iowa State University Digital Repository. For more information, please contact [email protected]. User Manual for Ox: An Attribute-Grammar Compiling System based on Yacc, Lex, and C Abstract Ox generalizes the function of Yacc in the way that attribute grammars generalize context-free grammars. Ordinary Yacc and Lex specifications may be augmented with definitions of synthesized and inherited attributes written in C syntax. From these specifications, Ox generates a program that builds and decorates attributed parse trees. Ox accepts a most general class of attribute grammars. The user may specify postdecoration traversals for easy ordering of side effects such as code generation. Ox handles the tedious and error-prone details of writing code for parse-tree management, so its use eases problems of security and maintainability associated with that aspect of translator development. The translators generated by Ox use internal memory management that is often much faster than the common technique of calling malloc once for each parse-tree node. -
UNIX X Command Tips and Tricks David B
SESUG Paper 122-2019 UNIX X Command Tips and Tricks David B. Horvath, MS, CCP ABSTRACT SAS® provides the ability to execute operating system level commands from within your SAS code – generically known as the “X Command”. This session explores the various commands, the advantages and disadvantages of each, and their alternatives. The focus is on UNIX/Linux but much of the same applies to Windows as well. Under SAS EG, any issued commands execute on the SAS engine, not necessarily on the PC. X %sysexec Call system Systask command Filename pipe &SYSRC Waitfor Alternatives will also be addressed – how to handle when NOXCMD is the default for your installation, saving results, and error checking. INTRODUCTION In this paper I will be covering some of the basics of the functionality within SAS that allows you to execute operating system commands from within your program. There are multiple ways you can do so – external to data steps, within data steps, and within macros. All of these, along with error checking, will be covered. RELEVANT OPTIONS Execution of any of the SAS System command execution commands depends on one option's setting: XCMD Enables the X command in SAS. Which can only be set at startup: options xcmd; ____ 30 WARNING 30-12: SAS option XCMD is valid only at startup of the SAS System. The SAS option is ignored. Unfortunately, ff NOXCMD is set at startup time, you're out of luck. Sorry! You might want to have a conversation with your system administrators to determine why and if you can get it changed. -
5 Command Line Functions by Barbara C
ADAPS: Chapter 5. Command Line Functions 5 Command Line Functions by Barbara C. Hoopes and James F. Cornwall This chapter describes ADAPS command line functions. These are functions that are executed from the UNIX command line instead of from ADAPS menus, and that may be run manually or by automated means such as “cron” jobs. Most of these functions are NOT accessible from the ADAPS menus. These command line functions are described in detail below. 5.1 Hydra Although Hydra is available from ADAPS at the PR sub-menu, Edit Time Series Data using Hydra (TS_EDIT), it can also be started from the command line. However, to start Hydra outside of ADAPS, a DV or UV RDB file needs to be available to edit. The command is “hydra rdb_file_name.” For a complete description of using Hydra, refer to Section 4.5.2 Edit Time-Series Data using Hydra (TS_EDIT). 5.2 nwrt2rdb This command is used to output rating information in RDB format. It writes RDB files with a table containing the rating equation parameters or the rating point pairs, with all other information contained in the RDB comments. The following arguments can be used with this command: nwrt2rdb -ooutfile -zdbnum -aagency -nstation -dddid -trating_type -irating_id -e (indicates to output ratings in expanded form; it is ignored for equation ratings.) -l loctzcd (time zone code or local time code "LOC") -m (indicates multiple output files.) -r (rounding suppression) Rules • If -o is omitted, nwrt2rdb writes to stdout; AND arguments -n, -d, -t, and -i must be present. • If -o is present, no other arguments are required, and the program will use ADAPS routines to prompt for them. -
Yacc a Tool for Syntactic Analysis
1 Yacc a tool for Syntactic Analysis CS 315 – Programming Languages Pinar Duygulu Bilkent University CS315 Programming Languages © Pinar Duygulu Lex and Yacc 2 1) Lexical Analysis: Lexical analyzer: scans the input stream and converts sequences of characters into tokens. Lex is a tool for writing lexical analyzers. 2) Syntactic Analysis (Parsing): Parser: reads tokens and assembles them into language constructs using the grammar rules of the language. Yacc is a tool for constructing parsers. Yet Another Compiler to Compiler Reads a specification file that codifies the grammar of a language and generates a parsing routine CS315 Programming Languages © Pinar Duygulu 3 Yacc • Yacc specification describes a Context Free Grammar (CFG), that can be used to generate a parser. Elements of a CFG: 1. Terminals: tokens and literal characters, 2. Variables (nonterminals): syntactical elements, 3. Production rules, and 4. Start rule. CS315 Programming Languages © Pinar Duygulu 4 Yacc Format of a production rule: symbol: definition {action} ; Example: A → Bc is written in yacc as a: b 'c'; CS315 Programming Languages © Pinar Duygulu 5 Yacc Format of a yacc specification file: declarations %% grammar rules and associated actions %% C programs CS315 Programming Languages © Pinar Duygulu 6 Declarations To define tokens and their characteristics %token: declare names of tokens %left: define left-associative operators %right: define right-associative operators %nonassoc: define operators that may not associate with themselves %type: declare the type of variables %union: declare multiple data types for semantic values %start: declare the start symbol (default is the first variable in rules) %prec: assign precedence to a rule %{ C declarations directly copied to the resulting C program %} (E.g., variables, types, macros…) CS315 Programming Languages © Pinar Duygulu 7 A simple yacc specification to accept L={ anbn | n>1}.