1. UNIX Shell Script (1) Dr. Tran, Van Hoai Faculty of Computer Science and Engineering HCMC Uni. of Technology [email_address]

3. Components of a script #!/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

9. Filename metacharacters Current working 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 *

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) Same as # 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 OR cmd1 || 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

18. Simple commands Create date 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