Bash Tips and Pitfalls: Difference between revisions
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Empty a file named <tt>filename</tt>, keeping the same permission and user/group: |
Empty a file named <tt>filename</tt>, keeping the same permission and user/group: |
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== Tips == |
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<source lang="bash"> |
<source lang="bash"> |
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...on 2 lines... |
...on 2 lines... |
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</source> |
</source> |
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== Pits == |
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{| class="wikitable" |
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!Description |
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!Example |
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|'''Space!''' - Don't forget to add spaces whenever necessary, in particular around brace in '''function''' definition, or in test conditions for '''if'''s. |
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<tt>if <font color="red">''-space-''</font> [ <font color="red">''-space-''</font> -f /etc/foo <font color="red">''-space-''</font> ]; then ...</tt><br/> |
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<tt>function myfunc() { <font color="red">''-space-''</font> echo Hello, World!; }</tt> |
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|'''Quote''' - Always quote parameters, variables passed to test in if ... then ... else: |
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<tt>if [ <font color="red">"$name"</font> -eq 5 ]; then ...</tt> |
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|'''For loops with file''' - Use simply '''*''' to list files in for loops, not <tt>`ls *`</tt>: |
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<source lang="bash" enclose="valid"> |
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for file in *; cat "$file"; done # SUCCEEDS, even if white space |
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for file in `ls *`; cat "$file"; done # FAILS miserably |
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</source> |
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|'''Space variable setting''' - There must be no space between the variable name and the subsequent equal sign. Also the variable name must not be prefixed with a <tt>$</tt> |
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<source lang="bash" enclose="valid"> |
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srcDir = $1 # WRONG - spaces around = sign |
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$srcDir=$1 # WRONG - variable name must not have $ prefix |
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srcDir=$1 # CORRECT |
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srcDir="$1" # BEST |
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</source> |
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|} |
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Revision as of 16:37, 22 January 2009
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 ... |
| 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
|