Shell Scrripts Tips-N-Tricks

The syntax and examples are written for use with bash (Bourne Again Shell) other shells may vary.

All script files must declare a shell on the first line.All the examples provided herein assume the first line is the following: #!/bin/bash Also, you must have execute permissions on the script file you create. You can give yourself execute permissions by typing the following: chmod u+x filename
Special Characters
#	comments
*	wildcard
?	single character wildcard
	redirect input - stdin
	redirect output - stdout
string comparisons
=	equal
!=	not equal
<	is less than
>	is greater than
-n	is not null
-z	is null
numeric comparisons
-eq	equal
-ge	greater than or equal to
-gt	greater than
-le	less than or equal to
-lt	less than
-ne	not equal
file operators
-d file	file exists and is directory
-e file	file exists
-f file	file exists and is regular
-s file	file exists and is not empty
file permission tests
-r file	you have read permission
-w file	you have write permission
-x file	you have execute permission
-O file	you have ownership
-G file	you have group ownership
file comparisons
file1 -nt file2	file1 newer than file2
file1 -ot file2	file1 older than file2
if then else statement
operators
-a	and
-o	or
Example: #!/bin/bash # if...then...else example # written by Elliott Technologies NUM=0 if [ $NUM -eq 0 ]; then echo true else echo false fi
while and case example:
#!/bin/bash # written by Elliott Technologies to demonstrate # a shell script that implements while and case # statements echo example of case val=1 while [ $val = 1 ] do echo -n "continue:" read userval case $userval in Yes|[Yy] ) # the above matches on Yes, Y, or y echo -n "you answered yes " ;; No|[Nn] ) # the above matches on No, N, or n echo Stopping since you answered no val=0 ;; * ) echo -n "please answer (Yes/No) " ;; esac done