Bash-Beginners-Guide

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[ -b FILE ] True if FILE exists and is a block-special file. [ -c FILE ] True if FILE exists and is a character-special file. [ -d FILE ] True if FILE exists and is a directory. [ -e FILE ] True if FILE exists. [ -f FILE ] True if FILE exists and is a regular file. [ -g FILE ] True if FILE exists and its SGID bit is set. [ -h FILE ] True if FILE exists and is a symbolic link. [ -k FILE ] True if FILE exists and its sticky bit is set. [ -p FILE ] True if FILE exists and is a named pipe (FIFO). [ -r FILE ] True if FILE exists and is readable. [ -s FILE ] True if FILE exists and has a size greater than zero. [ -t FD ] True if file descriptor FD is open and refers to a terminal. [ -u FILE ] True if FILE exists and its SUID (set user ID) bit is set. [ -w FILE ] True if FILE exists and is writable. [ -x FILE ] True if FILE exists and is executable. [ -O FILE ] True if FILE exists and is owned by the effective user ID. [ -G FILE ] True if FILE exists and is owned by the effective group ID. [ -L FILE ] True if FILE exists and is a symbolic link. [ -N FILE ] True if FILE exists and has been modified since it was last read. [ -S FILE ] True if FILE exists and is a socket. [ FILE1 -nt FILE2 ] [ FILE1 -ot FILE2 ] [ FILE1 -ef FILE2 ] [ -o OPTIONNAME ] True if FILE1 has been changed more recently than FILE2, or if FILE1 exists and FILE2 does not. True if FILE1 is older than FILE2, or is FILE2 exists and FILE1 does not. True if FILE1 and FILE2 refer to the same device and inode numbers. True if shell option "OPTIONNAME" is enabled. [ -z STRING ] True of the length if "STRING" is zero. [ -n STRING ] or [ STRING ] [ STRING1 == STRING2 ] [ STRING1 != STRING2 ] [ STRING1 < STRING2 ] [ STRING1 > STRING2 ] True if the length of "STRING" is non-zero. True if the strings are equal. "=" may be used instead of "==" for strict POSIX compliance. True if the strings are not equal. Bash Guide for Beginners True if "STRING1" sorts before "STRING2" lexicographically in the current locale. True if "STRING1" sorts after "STRING2" lexicographically in the current locale. "OP" is one of -eq, -ne, -lt, -le, -gt or -ge. These arithmetic binary operators return true if "ARG1" is equal to, not equal to, less than, less than or equal to, greater [ ARG1 OP ARG2 ] than, or greater than or equal to "ARG2", respectively. "ARG1" and "ARG2" are integers. Expressions may be combined using the following operators, listed in decreasing order of precedence: Chapter 7. Conditional statements 80
Bash Guide for Beginners Table 7-2. Combining expressions Operation Effect [ ! EXPR ] True if EXPR is false. [ ( EXPR ) ] [ EXPR1 -a EXPR2 ] Returns the value of EXPR. This may be used to override the normal precedence of operators. True if both EXPR1 and EXPR2 are true. [ EXPR1 -o EXPR2 True if either EXPR1 or EXPR2 is true. ] The [ (or test) built-in evaluates conditional expressions using a set of rules based on the number of arguments. More information about this subject can be found in the Bash documentation. Just like the if is closed with fi, the opening square bracket should be closed after the conditions have been listed. 7.1.1.2. Commands following the then statement The CONSEQUENT-COMMANDS list that follows the then statement can be any valid UNIX command, any executable program, any executable shell script or any shell statement, with the exception of the closing fi. It is important to remember that the then and fi are considered to be separated statements in the shell. Therefore, when issued on the command line, they are separated by a semi-colon. In a script, the different parts of the if statement are usually well-separated. Below, a couple of simple examples. 7.1.1.3. Checking files The first example checks for the existence of a file: anny ~> cat msgcheck.sh #!/bin/bash echo "This scripts checks the existence of the messages file." echo "Checking..." if [ -f /var/log/messages ] then echo "/var/log/messages exists." fi echo echo "...done." anny ~> ./msgcheck.sh This scripts checks the existence of the messages file. Checking... /var/log/messages exists. ...done. 7.1.1.4. Checking shell options To add in your Bash configuration files: # These lines will print a message if the noclobber option is set: Chapter 7. Conditional statements 81
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Bash Guide for Beginners Machtelt G
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Table of Contents Glossary C.......
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Introduction 1. Why this guide? The
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Revision 1.6 2005-03-01 Revised by:
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Bash Guide for Beginners See Chapte
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Bash Guide for Beginners mia:~> cat
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Bash Guide for Beginners When invok
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More information about the file des
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Built-in commands are necessary to
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• Brace expansion • Tilde expan
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A number of methods can be used; on
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Bash Guide for Beginners stop in ea
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Chapter 2. Writing and debugging sc
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the documentation of your favorite
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Bash Guide for Beginners Comments a
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Bash Guide for Beginners + set +x I
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Chapter 11. Functions In this chapt
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The commands after && are only exec
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zip2 "$TAR" echo "...done." >> "$LO
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Chapter 12. Catching signals In thi
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Bash Guide for Beginners maud: ~> k
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Bash Guide for Beginners 2. Write a
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Bash Guide for Beginners jobs kill
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if [ $i -eq 5 ] ArrowUp+Enter or !!
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cd Change directory. cdp/cdplay An
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Bash Guide for Beginners gimp grep
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Send and receive mail. man Read man
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Bash Guide for Beginners rsh RPM Pa
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W Bash Guide for Beginners w Show w
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Index A aliases Section 3.5.1 ANSI-
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Bash Guide for Beginners Section 3.
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J Bash Guide for Beginners K kill k
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eadonly Section 10.1.3 regular expr
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Bash Guide for Beginners vi(m) Sect
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