Talk Unix Shell Script 1

Talk Unix Shell Script 1

• 1.
  UNIX Shell Script(1) Dr. Tran, Van Hoai Faculty of Computer Science and Engineering HCMC Uni. of Technology [email_address]
• 2.
  What is ashell script? A series of OS commands for execution Stored in a text file #!/bin/sh rm -f /tmp/listing.tmp > /dev/null 2>&1 touch /tmp/listing.tmp ls -l [a-z]*.doc | sort > /tmp/listing.tmp lpr -Ppostscript_1 /tmp/listing.tmp rm -f /tmp/listing.tmp
• 3.
  Components of ascript #!/bin/sh rm -f /tmp/listing.tmp > /dev/null 2>&1 touch /tmp/listing.tmp # This is a comment ls -l [a-z]*.doc | sort > /tmp/listing.tmp lpr -Ppostscript_1 /tmp/listing.tmp rm -f /tmp/listing.tmp Shell in use (sh, bash, csh) Comment Command
• 4.
  How to invokea script Correct way $ /bin/bash my_script arg_1 arg_2 Simple way $ my_script arg_1 arg_2 The first line specifying the shell must be provided in simple way
• 5.
  How to behelped Man pages hoai@moon:~> man bash ... hoai@moon:~> man sh ...
• 6.
  Definitions Blank =chunk of tab or space Name = sequence of ASCII letters , digits , underscores , beginning with a letter or underscore Argument = string supplied on command-line
• 7.
  Example (argument) (1)#!/bin/sh ############################## echo "Script name is [$0]" echo "First argument is [$1]" echo "Second argument is [$2]" echo "This process ID is [$$]" echo "This argument count is [$#]" echo "All arguments [$@]"
• 8.
  Example (argument) (2)hoai@moon:~> my_script.sh hoai 1 university Script name is [my_script.sh] First argument is [hoai] Second argument is [1] This process ID is [5401] This argument count is [3] All arguments [hoai 1 university]
• 9.
  Filename metacharacters Currentworking directory ( $PWD ) ~+ Previous working directory ( $OLDPWD ) ~- Home directory of user name ~ name Home directory of the current user ~ Match any character not enclosed as above [! abc ...] Match any one of the enclosed characters; a hyphen can specify a range (e.g., a-z, A-Z, 0–9) [ abc ...] Match any single character ? Match any string of zero or more characters *
• 10.
  Simple regular expressions(Korn shell) Pattern = sequence of patterns separated by “|” Match any strings that don't match pattern !( pattern ) Match exactly one instance of pattern @( pattern ) Match one or more instances of pattern +( pattern ) Match zero or more instances of pattern *( pattern ) Match zero or one instance of pattern ?( pattern )
• 11.
  Example (metacharacters) Listfiles having prefix new $ ls new* Cat files having prefix ch and one more letter $ cat ch? Vi files starting by letters from D to E $ vi [D-R]* Print files not *.o and core (Korn shell) $ pr !(*.o|core) | lp
• 12.
  Quoting Charater following \ taken literally \ Everything taken literally '' Everything taken literally, except $ (variable substitution) ` (command substitution) “ (ending mark) ""
• 13.
  Example (quoting) $echo 'my class is "unix and tools"' My class is "unix and tools" $ echo "Well, isn't that \"good\" ?" Well, isn't that "good" ? $ echo "You have `ls | wc –l` files in `pwd`" You have 34 files in /home/hoai $ echo "The value of \$x is $x" The value of $x is 100
• 14.
  Variables (1) Use var if set, otherwise, print value and exit ${ var :? value } Use value of var is set, otherwise use nothing ${ var :+ value } Use the length of var ${# var } Use the number of positional arguments ${#*} or ${#@} Use var if set, otherwise, user value and assign it to var ${ var := value } Use var if set, otherwise, use value ${ var :- value } Use value of var ${ var } Set variable to value var=value …
• 15.
  Variables (2) Sameas # pattern . Remove longest matching ${ var ## pattern } Same as %pattern . Remove longest matching ${ var %% pattern } Use value of var after removing pattern from the right. Remove shortest matching ${ var % pattern } Use value of var after removing pattern from the left. Remove shortest matching ${ var # pattern }
• 16.
  Command forms ORcmd1 || cmd2 AND; cmd1, then cmd2 if (cmd succeeds) cmd1 && cmd2 POSIX shell arithmetic substitution cmd $((expression)) POSIX Command substitution (nesting is allowed) cmd1 $(cmd2) Command substitution cmd1 `cmd2` Pipe cmd1 | cmd2 NOT; change exit status ! cmd Commands as a group in a subshell ( cmd1 ; cmd2 ) Commands as a group in current shell { cmd1 ; cmd2 } Multiple commands on the same line cmd1 ; cmd2
• 17.
  Example (command forms)$ nroff file > file.txt & Format in the background $ cd; ls Execute sequentially $ (date; who; pwd) > logfile All output is redirected $ sort file | pr -3 | lp Sort file, page output, then print $ vi 'grep -l ifdef *.c' Edit files found by grep $ grep XX file && lp file Print file if it contains the pattern; $ grep XX file || echo "XX not found" otherwise, echo an error message
• 18.
  Simple commands Createdate strings date Evaluate variables eval Transform characters tr 'a' 'b' Simple arithmetic processor expr Predicate or conditional processor [( test )] Access lines in files head/tail Chop up a text by strings or characters cut Get directory name from path string dirname Get file name from path string basename Search for regular expressions grep Sort lines sort
• 19.
  Example (script) (1)#!/bin/bash alphabet="a b c d e" # Initialise a string count=0 # Initialise a counter for letter in $alphabet # Set up a loop control do # Begin the loop count=`expr $count + 1` # Increment the counter # Display the result echo "Letter $count is [$letter]" done
• 20.
  Example (script) (2)alphabet="a b c d e" # Initialise a string count=0 # Initialise a counter while [ $count -lt 5 ] # Set up a loop control do # Begin the loop count=`expr $count + 1` # Increment the counter # Position of next letter position=`bc $count + $count - 1` letter=`echo "$alphabet" | cut -c$position-$position` # Get next letter # Display the result echo "Letter $count is [$letter]" done
• 21.
  Homeworks (1) Writea script for C compiler Objective: use gcc by default, if gcc is not availablle, find another compiler (ending with cc ) instead. Write a script to convert filenames to lowercase letters Input: a directory path string Output: all filenames in the directory in lowercase
• 22.
  Homeworks (2) Writea script to warn users using too much space Objective: find all users of the system (/etc/passwd, cut), check if someone uses > 1GB, mail him a warning message
• 23.
  Conditional structure Loopstructure Function File input/output Array are NEXT