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How to Evaluate an Expresion in Shell Scripting Language |
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Next example evaluates if a=100, and if is true, it will echo a:
If evaluation example #!/bin/sh a=100 if [ "$a" -eq 100 ] then fi
Here are some evaluation operators (comparissons):
-eq --- is equal to
-ne --- is not equal to
-gt --- is greater then
-ge --- is greater then or equal to
-lt --- is less then
-le --- is less then or equal to
= --- is equal to, valid for string comparisons.
File operations (verify if):
-f --- file exists and is not a directory
-d --- directory exists
-s --- file exists and is not empty
-x --- file is executable
-r --- file is readable
-w --- file is writable
The followig example print "File exists" message, if a file install.log exists in the same directory as the script:
example2.sh #!/bin/sh echo "Now I will verify if file install.log exists:" if [ -f "install.log" ] then fi
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Shell Programming 
