bash
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bash [2012/10/12 16:52] k2patel [Control case] |
bash [2020/08/10 02:35] (current) |
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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. | ||
| Line 271: | Line 271: | ||
| </code> | </code> | ||
| + | |||
| + | ==== Bash alias and complition ==== | ||
| + | Using command completion for alias in bash. | ||
| + | <code bash ~/.bash_profile> | ||
| + | alias c='/usr/bin/ssh' | ||
| + | export HLIST | ||
| + | HLIST=`cat ~/.ssh/known_hosts | cut -f 1 -d ' ' | sed -e s/,.*//g | uniq | grep -v "\["` | ||
| + | HLIST="${HLIST} $(cat ~/.ssh/config | grep Host | awk '{print $2}' | grep -v \*)" | ||
| + | HLIST=$(echo ${HLIST} | sort | uniq) | ||
| + | complete -W "${HLIST}" c | ||
| + | </code> | ||
| ==== Control case ==== | ==== Control case ==== | ||
| Line 352: | Line 363: | ||
| ==== Bash Tips / Tricks ==== | ==== 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 ==== | ||
bash.1350060772.txt.gz ยท Last modified: 2020/08/10 02:28 (external edit)
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