program_lang:bash
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program_lang:bash [2022/06/19 08:34] manu [basename] |
program_lang:bash [2024/04/17 16:06] (current) manu |
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| ====== BASH ====== | ====== BASH ====== | ||
| + | |||
| + | ===== IF ===== | ||
| + | |||
| + | if or compare text | ||
| + | if [ "$fname" = "a.txt" ] || [ "$fname" = "c.txt" ] | ||
| + | if [ $a == $b -o $b == $c -o $a == $c ] | ||
| + | | ||
| + | if and | ||
| + | if [ $a == $b -a $b == $c -a $a == $c ] | ||
| + | if [ "$fname" = "a.txt" ] && [ "$fname" = "c.txt" ] | ||
| + | |||
| + | ===== Use CSV file ===== | ||
| + | |||
| + | ==== Change column order ==== | ||
| + | |||
| + | Switch column 1 and 3 serared by ; | ||
| + | <cli prompt='#'> | ||
| + | [root@lnx01 ~]# echo "1;2;3;4;5" | awk -F';' '{ t = $3 ; $3 = $1; $1 = t; print; }' OFS=';' | ||
| + | 3;2;1;4;5 | ||
| + | </cli> | ||
| ===== backup files and folders permissions ===== | ===== backup files and folders permissions ===== | ||
| Line 99: | Line 119: | ||
| arr=( $(ls) ) Save ls output as an array of files | arr=( $(ls) ) Save ls output as an array of files | ||
| ${arr[@]:s:n} Retrieve n elements starting at index s | ${arr[@]:s:n} Retrieve n elements starting at index s | ||
| + | |||
| + | Exemple | ||
| + | <cli prompt='#'> | ||
| + | #!/usr/bin/bash | ||
| + | declare -a Users=('user01' '1001' '1000' '' '' '/bin/bash') | ||
| + | Users+=('user02' '1002' '1003' '' '' '/bin/bash') | ||
| + | Users+=('user03' '1003' '4' 'Recovery user' '' '/bin/bash') | ||
| + | |||
| + | UserNbProps=6 | ||
| + | let NbUsers=${#Users[@]}/$UserNbProps | ||
| + | |||
| + | for (( i=0; i<$NbUsers; i++ )) | ||
| + | do | ||
| + | let ArrayIndex=i*UserNbProps | ||
| + | Line=$(cat /etc/passwd | grep "^${Users[$ArrayIndex]}:") | ||
| + | if [ -z "$Line" ] | ||
| + | then | ||
| + | echo "# ${Users[$ArrayIndex]} user was not found" | ||
| + | else | ||
| + | Uid=$(echo $Line | cut -d: -f3) | ||
| + | Gid=$(echo $Line | cut -d: -f4) | ||
| + | UidRef=${Users[$ArrayIndex+1]} | ||
| + | GidRef=${Users[$ArrayIndex+2]} | ||
| + | if [ $Uid != $UidRef -o $Gid != $GidRef ] | ||
| + | then | ||
| + | echo "# User: ${Users[$ArrayIndex]} uid:$Uid gid:$Gid does not match reference uid:$UidRef gid:$GidRef" | ||
| + | fi | ||
| + | fi | ||
| + | done | ||
| + | </cli> | ||
| | | ||
| ===== Read files ===== | ===== Read files ===== | ||
| Line 111: | Line 161: | ||
| awk 'NR>1' myfile.txt | awk 'NR>1' myfile.txt | ||
| | | ||
| + | ===== trap ===== | ||
| + | |||
| + | The format of the trap command is: | ||
| + | <cli prompt='#'> | ||
| + | # trap 'command_list' signals | ||
| + | </cli> | ||
| + | |||
| + | To ignore a signal, use two single quotes in place of the command_list: | ||
| + | <cli prompt='#'> | ||
| + | # trap '' signals | ||
| + | </cli> | ||
| + | |||
| + | To reset a trap use: | ||
| + | <cli prompt='#'> | ||
| + | # trap ‑ signals | ||
| + | </cli> | ||
| + | |||
| + | **Example** | ||
| + | <cli> | ||
| + | #!/bin/bash | ||
| + | #trapoff_on | ||
| + | |||
| + | trap '' SIGINT SIGQUIT | ||
| + | echo "you cannot terminate using ctrl‑c or ctrl‑\, " | ||
| + | #heavy pressing go on here, cannot interrupt ! | ||
| + | sleep 10 | ||
| + | |||
| + | trap 'echo terminated; exit' SIGINT SIGQUIT | ||
| + | #user can now interrupt | ||
| + | echo "ok you can now terminate me using those keystrokes" | ||
| + | sleep 10 | ||
| + | </cli> | ||
| + | |||
| + | Example, to remove a file | ||
| + | <cli> | ||
| + | trap 'rm /tmp/hold∗.$$; exit' SIGNHUP SIGINT SIGQUIT SIGTERM | ||
| + | </cli> | ||
| + | |||
| + | === For info === | ||
| + | |||
| + | To view the signals and their default actions (on an AIX machine), view the file: | ||
| + | <cli prompt='$'> | ||
| + | $ cat /usr/include/sys/signal.h | more | ||
| + | ….. | ||
| + | ….. | ||
| + | #define SIGHUP 1 /∗ hangup, generated when terminal disconnects ∗/ | ||
| + | #define SIGINT 2 /∗ interrupt, generated from terminal special char ∗/ | ||
| + | #define SIGQUIT 3 /∗ (∗) quit, generated from terminal special char ∗/ | ||
| + | #define SIGILL 4 /∗ (∗) illegal instruction (not reset when caught)∗/ | ||
| + | #define SIGTRAP 5 /∗ (∗) trace trap (not reset when caught) ∗/ | ||
| + | #define SIGABRT 6 /∗ (∗) abort process ∗/ | ||
| + | ... | ||
| + | </cli> | ||
| + | |||
| + | You can use either signal name or signal number. | ||
| + | |||
| + | === I have received a signal. Now what? === | ||
| + | |||
| + | When a signal has been received by the script, the script can do one of three actions: | ||
| + | * Ignore it and do nothing. This is probably what most scripts do without the script authors realising it. | ||
| + | * Catch the signal using trap and take appropriate action. | ||
| + | * Take the default action. | ||
| + | |||
| + | All the above is true except for the following signals: | ||
| + | * SIGKILL (signal 9) | ||
| + | * SIGSTOP(signal 17) | ||
| + | * SIGCONT (signal 19) | ||
program_lang/bash.1655620473.txt.gz · Last modified: 2022/06/19 08:34 by manu
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