Bash Tips and Pitfalls

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Revision as of 16:37, 22 January 2009 by Mip (talk | contribs) (Added pitfalls)
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Empty a file named filename, keeping the same permission and user/group:

Tips

>filename

Print multi-lines text with echo:

$ echo -e "Some text\n...on 2 lines..."                    # Enable interpretation of backslash escapes (must be quoted!)
Some text
...on 2 lines...

Pits

Description Example
Space! - Don't forget to add spaces whenever necessary, in particular around brace in function definition, or in test conditions for ifs.

if -space- [ -space- -f /etc/foo -space- ]; then ...
function myfunc() { -space- echo Hello, World!; }

Quote - Always quote parameters, variables passed to test in if ... then ... else:

if [ "$name" -eq 5 ]; then ...

For loops with file - Use simply * to list files in for loops, not `ls *`:
for file in *; cat "$file"; done       # SUCCEEDS, even if white space
for file in `ls *`; cat "$file"; done  # FAILS miserably
Space variable setting - There must be no space between the variable name and the subsequent equal sign. Also the variable name must not be prefixed with a $
srcDir = $1        # WRONG - spaces around = sign
$srcDir=$1         # WRONG - variable name must not have $ prefix
srcDir=$1          # CORRECT
srcDir="$1"        # BEST