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Submitted by:
lvo |
coolcommand
how to use the test command to check files and variables |
Description
The test command allows you to test files and variables in your shell scripts:
# test expression
OR
[ expression ]
Flags for file testing:
-r : True if file exists and is readable
-w : True if file exists and is writable
-x : True if file exists and is executable
-f : True if file exists and is a regular file
-d : True if file exists and is a directory
-c : True if file exists and is a character special file
-b : True if file exists and is a block special file
-p : True if file exists and is a named pipe (FIFO)
-u : True if file exists and is a SETUID file
-g : True if file exists and is a SETGID file
-k : True if file exists and the sticky bit is set
-s : True if file exists and has a size greater than zero
Logical expressions:
! : Not
-a : And
-o : Or (has lower precedence that -a)
\( \) : Parentheses for grouping
Relational operators:
-ne : Not equal
-eq : Equal
-gt : Greater then
-ge : Greater than or equal
-le : Less than or equal
-lt : Less than
Strings comparison:
-z str : True if string length is zero
-n str : True if string length is non-zero
str1 = str2 : True if strings are identical. NOte that this uses a single = symbol unlike C's equality operator.
str1 != str2 : True if strings are not identical
str : True if string is not the null string
Examples:
if [ ! -r $1 ]
then
echo File $1 does not exist or is not readable
exit
fi
for i in *
do
if [ -d $i ]
then
echo $i
fi
done
[ $VERBOSE -eq 1 ] && echo "This is verbose output"
|
Example
test expression |
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Friday May 24, 2013
