{"id":1775,"date":"2014-01-25T14:55:32","date_gmt":"2014-01-25T14:55:32","guid":{"rendered":"http:\/\/blog.bachi.net\/?p=1775"},"modified":"2024-03-08T21:09:42","modified_gmt":"2024-03-08T21:09:42","slug":"bash-scripting","status":"publish","type":"post","link":"https:\/\/blog.bachi.net\/?p=1775","title":{"rendered":"Bash scripting"},"content":{"rendered":"

<\/p>\n

Keyboard shortcuts<\/h3>\n

Command Line Editing<\/a>
\nCommands For Moving<\/a>
\nMastering The Linux Shell \u2013 Bash Shortcuts Explained (Now With Cheat Sheets)<\/a>
\nBash Keyboard Shortcuts<\/a><\/p>\n

\r\n[CTRL + P]      Print previous command (Up arrow)\r\n[CTRL + N]      Print next command (Down arrow)\r\n[CTRL + R]      History search\r\n[ALT  + R]      Cancel changes, put back like in the history\r\n[!    + !]      Repeat last command\r\n[!    + <cmd>]  Run last command starting with <cmd>\r\n[!    + *]      Run all argument of previous command\r\n[!    + $]      Run last argument of previous command\r\n[ALT  + .]      Print last argument of previous command\r\n[^<p1> + ^<p2>] Run last command, replace <p1> with <p2>\r\n<\/pre>\n
\r\n[CTRL + F]      Move forward one character (Right arrow)\r\n[CTRL + B]      Move backward one character (Left arrow)\r\n\r\n[ALT  + F]      Move forward one word\r\n[ALT  + B]      Move backward one word\r\n\r\n[CTRL + A]      Move to the start of the line\r\n[CTRL + E]      Move to the end of the line\r\n\r\n[CTRL + X + X]  Toggle between start of word and cursor\r\n<\/pre>\n
\r\n[CTRL + H]      Delete previous character from the cursor\r\n                (= Rubout, like Backspace)\r\n[CTRL + D]      Delete current character from the cursor (Delete)\r\n<\/pre>\n
\r\n[CTRL + K]      Cut from the cursor to the end of the line\r\n[CTRL + U]      Cut from the cursor to the start of the line\r\n                (like [CTRL + X + BACKSPACE]\r\n\r\n[ALT  + D]      Cut from the cursor to the end of the current word\r\n[CTRL + W]      Cut from the cursor to the previous whitespace\r\n\r\n[CTRL + Y]      Paste\r\n<\/pre>\n
\r\n[ALT  + T]      Swap current word with previous (or [ESC + T])\r\n[CTRL + T]      Swap the last two characters before the cursor (typo)\r\n\r\n[ALT  + U]      Upper-case word and move to the end of the word\r\n[ALT  + L]      Lower-case word and move to the end of the word\r\n[ALT  + C]      Capitalize word and move to the end of the word\r\n<\/pre>\n
<\/p>\n
Job ID \/ Percent sign (%)<\/h3>\n
Percent sign (%) in front of shell command<\/a><\/p>\n
\r\n$ tail -f \/var\/log\/messages\r\n[CTRL + Z]\r\n[1]+  Stopped                 tail -f \/var\/log\/messages\r\n\r\n$ tail -f \/var\/log\/maillog\r\n[CTRL + Z]\r\n[2]+  Stopped                 tail -f \/var\/log\/maillog\r\n\r\n$ jobs\r\n[1]-  Stopped                 tail -f \/var\/log\/messages\r\n[2]+  Stopped                 tail -f \/var\/log\/maillog\r\n\r\n$ fg %2\r\ntail -f \/var\/log\/maillog\r\n[CTRL + Z]\r\n[2]+  Stopped                 tail -f \/var\/log\/maillog\r\n\r\n$ fg %1\r\ntail -f \/var\/log\/messages\r\n[CTRL + Z]\r\n[1]+  Stopped                 tail -f \/var\/log\/messages\r\n\r\n$ kill %1 %2\r\n[1]-  Terminated              tail -f \/var\/log\/messages\r\n[2]+  Terminated              tail -f \/var\/log\/maillog\r\n<\/pre>\n
<\/p>\n
Simple commands<\/strong> vs Compound commands<\/strong><\/h3>\n
What is the essential difference between compound command and normal command in bash?<\/a><\/p>\n
four types of compound commands:<\/p>\n\n\n\n\n\n\n
Funktion<\/td>\nErkl\u00e4rung<\/td>\n<\/tr>\n
Group: {...;}<\/code><\/td>\ncan be used to group simple commands together to form a compound command.<\/td>\n<\/tr>\n
Subshell: (...)<\/code><\/td>\nis similar to a group except that the commands are run in subshell environment.<\/td>\n<\/tr>\n
Arithmetic Expression: ((..))<\/code><\/td>\na series of comma-separated arithmetic calculations may be performed.<\/td>\n<\/tr>\n
Test Command: [[...]]<\/code><\/td>\nadvanced form of the test command.<\/td>\n<\/tr>\n<\/table>\n
<\/p>\n
Bash Brackets Quick Reference<\/h3>\n
Bash Brackets Quick Reference<\/a>
\nHow to use double or single brackets, parentheses, curly braces<\/a>
\nWhen do we need curly braces around shell variables?<\/a>
\nDifferences Between Single and Double Brackets in Bash<\/a><\/p>\n
\r\n( Single Parentheses )\r\n(( Double Parentheses ))\r\n<( Angle Parentheses )\r\n$( Dollar Single Parentheses )\r\n$( Dollar Single Parentheses Dollar Q )$?\r\n$(( Dollar Double Parentheses ))\r\n[ Single Square Brackets ]\r\n[[ Double Square Brackets ]]\r\n{ Single Curly Braces }\r\n${Dollar Braces}\r\n<<Double Angle Heredocs\r\n<\/pre>\n
<\/p>\n
if [ ]<\/h3>\n
File based<\/p>\n\n\n\n\n\n\n\n\n\n\n\n\n\n\n\n\n\n\n\n\n\n\n\n\n\n\n\n\n
Primary<\/th>\nMeaning<\/th>\n<\/tr>\n<\/thead>\n
[ -a<\/tt> FILE<\/tt> ]<\/td>\nTrue if FILE<\/tt> exists.<\/td>\n<\/tr>\n
[ -b<\/tt> FILE<\/tt> ]<\/td>\nTrue if FILE<\/tt> exists and is a block-special file.\n            <\/td>\n<\/tr>\n
[ -c<\/tt> FILE<\/tt> ]<\/td>\nTrue if FILE<\/tt> exists and is a character-special
\n                file.<\/td>\n<\/tr>\n
[ -d<\/tt> FILE<\/tt> ]<\/td>\nTrue if FILE<\/tt> exists and is a directory.<\/td>\n<\/tr>\n
[ -e<\/tt> FILE<\/tt> ]<\/td>\nTrue if FILE<\/tt> exists.<\/td>\n<\/tr>\n
[ -f<\/tt> FILE<\/tt> ]<\/td>\nTrue if FILE<\/tt> exists and is a regular file.<\/td>\n<\/tr>\n
[ -g<\/tt> FILE<\/tt> ]<\/td>\nTrue if FILE<\/tt> exists and its SGID bit is set.<\/td>\n<\/tr>\n
[ -h<\/tt> FILE<\/tt> ]<\/td>\nTrue if FILE<\/tt> exists and is a symbolic link.<\/td>\n<\/tr>\n
[ -k<\/tt> FILE<\/tt> ]<\/td>\nTrue if FILE<\/tt> exists and its sticky bit is set.\n            <\/td>\n<\/tr>\n
[ -p<\/tt> FILE<\/tt> ]<\/td>\nTrue if FILE<\/tt> exists and is a named pipe (FIFO).\n            <\/td>\n<\/tr>\n
[ -r<\/tt> FILE<\/tt> ]<\/td>\nTrue if FILE<\/tt> exists and is readable.<\/td>\n<\/tr>\n
[ -s<\/tt> FILE<\/tt> ]<\/td>\nTrue if FILE<\/tt> exists and has a size greater than
\n                zero.<\/td>\n<\/tr>\n
[ -t<\/tt> FD<\/tt> ]<\/td>\nTrue if file descriptor FD<\/tt> is open and refers to
\n                a terminal.<\/td>\n<\/tr>\n
[ -u<\/tt> FILE<\/tt> ]<\/td>\nTrue if FILE<\/tt> exists and its SUID (set user ID)
\n                bit is set.<\/td>\n<\/tr>\n
[ -w<\/tt> FILE<\/tt> ]<\/td>\nTrue if FILE<\/tt> exists and is writable.<\/td>\n<\/tr>\n
[ -x<\/tt> FILE<\/tt> ]<\/td>\nTrue if FILE<\/tt> exists and is executable.<\/td>\n<\/tr>\n
[ -O<\/tt> FILE<\/tt> ]<\/td>\nTrue if FILE<\/tt> exists and is owned by the effective
\n                user ID.<\/td>\n<\/tr>\n
[ -G<\/tt> FILE<\/tt> ]<\/td>\nTrue if FILE<\/tt> exists and is owned by the effective
\n                group ID.<\/td>\n<\/tr>\n
[ -L<\/tt> FILE<\/tt> ]<\/td>\nTrue if FILE<\/tt> exists and is a symbolic link.<\/td>\n<\/tr>\n
[ -N<\/tt> FILE<\/tt> ]<\/td>\nTrue if FILE<\/tt> exists and has been modified since
\n                it was last read.<\/td>\n<\/tr>\n
[ -S<\/tt> FILE<\/tt> ]<\/td>\nTrue if FILE<\/tt> exists and is a socket.<\/td>\n<\/tr>\n
[ FILE1<\/tt> -nt<\/tt> FILE2<\/tt> ]<\/td>\nTrue if FILE1<\/tt> has been changed more recently than
\n                FILE2<\/tt>, or if FILE1<\/tt> exists and FILE2<\/tt> does not.<\/td>\n<\/tr>\n
[ FILE1<\/tt> -ot<\/tt> FILE2<\/tt> ]<\/td>\nTrue if FILE1<\/tt> is older than FILE2<\/tt>, or is FILE2<\/tt> exists and FILE1<\/tt> does not.<\/td>\n<\/tr>\n
[ FILE1<\/tt> -ef<\/tt> FILE2<\/tt> ]<\/td>\nTrue if FILE1<\/tt> and FILE2<\/tt>
\n                refer to the same device and inode numbers.<\/td>\n<\/tr>\n<\/tbody>\n<\/table>\n
String based<\/p>\n\n\n\n\n\n\n\n\n\n\n\n\n
Primary<\/th>\nMeaning<\/th>\n<\/tr>\n<\/thead>\n
[ -o<\/tt> OPTIONNAME ]<\/td>\nTrue if shell option “OPTIONNAME”<\/span> is enabled.\n            <\/td>\n<\/tr>\n
[ -z<\/tt> STRING ]<\/td>\nTrue of the length if “STRING”<\/span> is zero.<\/td>\n<\/tr>\n
[ -n<\/tt> STRING ] or [ STRING ]<\/td>\nTrue if the length of “STRING”<\/span> is non-zero.<\/td>\n<\/tr>\n
[ STRING1 == STRING2 ] <\/td>\nTrue if the strings are equal. “=”<\/span> may be used
\n                instead of “==”<\/span> for strict POSIX compliance.<\/td>\n<\/tr>\n
[ STRING1 != STRING2 ] <\/td>\nTrue if the strings are not equal.<\/td>\n<\/tr>\n
[ STRING1 < STRING2 ] <\/td>\nTrue if “STRING1”<\/span> sorts before “STRING2”<\/span> lexicographically in the current locale.<\/td>\n<\/tr>\n
[ STRING1 > STRING2 ] <\/td>\nTrue if “STRING1”<\/span> sorts after “STRING2”<\/span> lexicographically in the current locale.<\/td>\n<\/tr>\n
[ ARG1 OP ARG2 ]<\/td>\n“OP”<\/span> is one of -eq<\/tt>, -ne<\/tt>, -lt<\/tt>, -le<\/tt>, -gt<\/tt> or -ge<\/tt>. These arithmetic binary operators return
\n                true if “ARG1”<\/span> is equal to, not equal to, less than, less than or equal to,
\n                greater than, or greater than or equal to “ARG2”<\/span>, respectively. “ARG1”<\/span> and “ARG2”<\/span> are integers.<\/td>\n<\/tr>\n<\/tbody>\n<\/table>\n
<\/p>\n
Process List (ps)<\/h3>\n
\r\n$ ps auxf\r\n<\/pre>\n
\r\n$ ps auxd\r\n<\/pre>\n
<\/p>\n
#!\/usr\/bin\/env<\/h3>\n
Howto Make Script More Portable With #!\/usr\/bin\/env As a Shebang<\/a><\/p>\n
\r\n#!\/usr\/bin\/env bash\r\n\r\nrather than\r\n\r\n#!\/bin\/bash\r\n<\/pre>\n
Bash Conditional Expressions<\/a>
\nThe Set Builtin<\/a><\/p>\n
<\/p>\n
Glob and Wildcard<\/h3>\n
glob<\/a>
\nQuotes<\/a>
\nArrays<\/a><\/p>\n
What if a Wildcard Doesn’t Match?<\/a>
\nWhy does using double brackets “[[” to check if wildcard matched files exists fail, while single brackets “[” work?<\/a>
\nTest if there are files matching a pattern in order to execute a script<\/a>
\nTest whether a glob has any matches in Bash<\/a>
\nThink You Understand Wildcards? Think Again.<\/a>
\nhow to handle bash * matching when there are no matches?<\/a>
\n<\/a><\/p>\n
\r\nshopt -s nullglob\r\nset -- *.txt\r\nif [ "$#" -gt 0 ]; then\r\n  .\/script "$@" # call script with that list of files.\r\nfi\r\n\r\n# Or with bash arrays so you can keep the arguments:\r\nfiles=( *.txt )\r\n# apply C-style boolean on member count\r\n(( ${#files[@]} )) && .\/script "${files[@]}"\r\n\r\n# Or with Bash built-in function\r\ncompgen -G "<glob-pattern>"\r\n\r\nif compgen -G "\/tmp\/someFiles*" > \/dev\/null; then\r\n    echo "Some files exist."\r\nfi\r\n<\/pre>\n
<\/p>\n
Arrays<\/h3>\n
6.7 Arrays<\/a>
\nYou don’t know Bash: An introduction to Bash arrays<\/a><\/p>\n