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bash [2012/07/05 14:35] k2patel [Networked Info] |
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[ FILE1 -ef FILE2 ] True if FILE1 and FILE2 refer to the same device and inode numbers. | [ FILE1 -ef FILE2 ] True if FILE1 and FILE2 refer to the same device and inode numbers. | ||
[ -o OPTIONNAME ] True if shell option "OPTIONNAME" is enabled. | [ -o OPTIONNAME ] True if shell option "OPTIONNAME" is enabled. | ||
- | [ -z STRING ] True of the length if "STRING" is zero. | + | [ -z STRING ] True if the length of "STRING" is zero. |
[ -n STRING ] or [ STRING ] True if the length of "STRING" is non-zero. | [ -n STRING ] or [ STRING ] True if the length of "STRING" is non-zero. | ||
[ STRING1 == STRING2 ] True if the strings are equal. "=" may be used instead of "==" for strict POSIX compliance. | [ STRING1 == STRING2 ] True if the strings are equal. "=" may be used instead of "==" for strict POSIX compliance. | ||
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To turn off a declare attribute, use "+". For example, declare +c string. This affects subsequent assignments and not the current value. | To turn off a declare attribute, use "+". For example, declare +c string. This affects subsequent assignments and not the current value. | ||
+ | ==== Bash Tips / Tricks ==== | ||
+ | === Quating === | ||
+ | Bash has a special form of quoting, $'string' in which backslash-character combinations are expanded. For example, echo $'this is a literal tab: \t' | ||
+ | <code bash> | ||
+ | re='foo.*bar'; [[ $'foo\nbar' =~ $re ]] && echo 'yes' || echo 'no' | ||
+ | </code> | ||
+ | === History Size === | ||
+ | <code bash> | ||
+ | HISTSIZE=1500000 | ||
+ | HISTFILESIZE=1500000 | ||
+ | HISTTIMEFORMAT="[%Y-%m-%d - %H:%M:%S] - " | ||
+ | </code> | ||
+ | |||
+ | === Truth Table === | ||
+ | <code bash> | ||
+ | These two commands not the same: | ||
+ | |||
+ | command1 && command2 || command3 | ||
+ | |||
+ | if command1 | ||
+ | then | ||
+ | command2 | ||
+ | else | ||
+ | command3 | ||
+ | fi | ||
+ | </code> | ||
+ | |||
+ | In the if-then-else, exactly one of command2 or command3 will be executed. But in the && || version, command3 runs if either command1 or command2 returns false. | ||
+ | |||
+ | <code bash> | ||
+ | for c1 in true false; do for c2 in true false; do echo "$c1 && $c2 || c3"; (echo c1; $c1) && (echo c2; $c2) || echo c3; done; done | ||
+ | </code> | ||
+ | |||
+ | And the output: | ||
+ | |||
+ | <code bash> | ||
+ | true && true || c3 | ||
+ | c1 | ||
+ | c2 | ||
+ | true && false || c3 | ||
+ | c1 | ||
+ | c2 | ||
+ | c3 | ||
+ | false && true || c3 | ||
+ | c1 | ||
+ | c3 | ||
+ | false && false || c3 | ||
+ | c1 | ||
+ | c3 | ||
+ | </code> | ||
+ | [[ http://www.linkedin.com/groups/Tuesdays-tip-difference-between-if-3716796.S.236851680?view=&srchtype=discussedNews&gid=3716796&item=236851680&type=member&trk=eml-anet_dig-b_pd-ttl-cn&ut=0FCRGmx_LdW5I1 | Link to Article ]] | ||
==== Networked Info ==== | ==== Networked Info ==== | ||