bash 4.0 – new feature mapfile

Recently I encountered a problem where I had to create couple of arrays in bash and these were quite dynamic in nature. This script was supposed to be used by couple of guys whom I did not trust too much in opening the script and modifyikng the array. So, the solution was to put these in different files and then put them in array using bash script itself. This is when I went through the bash man page again and found an interesting new inbuilt mapfile

perl is faster than bash in some cases.

Some days back, I had to generate some data to be uploaded to a database. As usual I assumed that bash should be faster and hence wrote the script to create the files in bash. But I found that even after 5 hours I was only 10% done with the data generation. Now that would mean that it would take around 50 hours to complete the data generation. Something did not look correct to me and I asked one of my colleague. He suggested I do a strace.

Shell Scripting

Here are some links for bash programming that you may find useful.

http://tips-linux.net/en/content/pro-bash-programming

http://tips-linux.net/en/content/expert-shell-scripting

http://tips-linux.net/en/content/beginning-linux-command-line

http://tips-linux.net/en/content/bash-pocket-reference

http://tips-linux.net/en/content/linux-command-line-and-shell-scripting-bible

Related articles

• Linux – Learning the Shell (edugeek.net)
• 10 Useful Tools, Websites And Tricks to Help You Master Linux Command (maketecheasier.com)
• lf-submit.sh – Bash mplayer Last.fm scrobbler (yjl.im)
• Linux command line tricks you need to know: IO redirection and piping (interstellr.com)
• imabonehead: Houcem HACHICHA’s Blog: My top ten shell/bash tricks! (houcemhachicha.blogspot.com)

Execute a command with a timeout

Execute a command with a timeout

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      &nbsp;timelimit -t100 somecommand
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I found this in Ubuntu repos, and consider it better than timeout.

* View this command to comment, vote or add to favourites * View all commands by CodSpirit

write the output of a command to /var/log/user.log… each line will contain $USER, making this easy to grep for.

write the output of a command to /var/log/user.log… each line will contain $USER, making this easy to grep for.

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      &nbsp;log() { (echo "$ $@";$@) | logger -t $USER; }
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This command is useful if you want to copy the output of a series of commands to a file, for example if you want to pastebin the output from ‘uname -a’, ‘lspci -vvv’ and ‘lsmod’ for video driver trouble-shooting on your favorite Linux forum.

Bash Script Beautifier

Today I was working on a bash script written by someone else. And the script was maintained since long and had actually become quite big and there was no indentation followed. So, you can understand how difficult it was to understand the script. So, I set my foot forth to first find a beautifier for the bash script before I fixed it and my search ended here.

Take a screenshot of the window the user clicks on and name the file the same as the window title

Take a screenshot of the window the user clicks on and name the file the same as the window title

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      &nbsp;sleep 4; xwd >foo.xwd; mv foo.xwd "$(dd skip=100 if=foo.xwd bs=1 count=256 2>/dev/null | egrep -ao '^[[:print:]]+' | tr / :).xwd"
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In general, this is actually not better than the “scrot -d4” command I’m listing it as an alternative to, so please don’t vote it down for that. I’m adding this command because xwd (X window dumper) comes with X11, so it is already installed on your machine, whereas scrot probably is not. I’ve found xwd handy on boxen that I don’t want to (or am not allowed to) install packages on.