Bash test: Difference between revisions
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| Line 36: | Line 36: | ||
=String Comparison= | =String Comparison= | ||
< and > can be used for string comparison, in ASCII alphabetical order, but | < and > can be used for string comparison, in ASCII alphabetical order, but <pre>[[ ... ]]</pre> must be used: | ||
<pre> | |||
if [[ "${a}" > "${b}" ]]; them | |||
... | |||
fi | |||
</pre> | |||
=-z, -n= | =-z, -n= | ||
Revision as of 02:46, 3 September 2016
External
Internal
Negation
[ ! -f ${file} ] && echo "we're not a file" || echo "we're a file"
-f
-w
True if file exists and is writable.
-h
Tests whether the file exists and it is a symbolic link.
[ -h $0 ] && echo "we're a link" || echo "we're not a link"
Integer Comparison
[arg1 -eq|-ne|-lt|-le|-gt|-ge arg2]
String Comparison
< and > can be used for string comparison, in ASCII alphabetical order, but
[[ ... ]]
must be used:
if [[ "${a}" > "${b}" ]]; them
...
fi
-z, -n
-z: true if the length of the string is zero.
-n: true if the length of string is non-zero.
Can be used to check for undeclared variables
[ -z ${var} ] && echo" 'var' not declared"
- Quotation marks around the variables are needed, otherwise the expression will fail syntactically when the variable is declared and it contains a space:
var="a b" ... line 177: [: 900: binary operator expected
Combining test and Command Conditionals
Not sure if this belongs here, refactor with https://home.feodorov.com:9443/wiki/Wiki.jsp?page=bashConditionalConstructs
verbose=false
if ! ${verbose} && [ "$1" = "--verbose" -o "$1" = "-v" ]; then
echo "setting verbose to ON"
fi
- Must have a space between ! and the command that evaluates to true or false.