the fancy part of the web » shell

bash: small improvement for the “cd” builtin

tolleiv — Thu, 18 Jun 2009 21:54:34 +0000

If you use the shell and walk around in directories wouldn’t it be cool to have “cd …” to move 2 levels up, “cd ….” to move 3 levels up …? I’m not sure if there’s an easier way to resolve it but the following lines work pretty nice so far and they just made it into my default .bashrc

cd() {
	if [[ "$1" =~ ^\.\.\.+$  ]]; then
		cd `echo "$1" | sed 's/\./..\//g' | sed 's/^\.\.\///g'`
	else
		builtin cd "$1"
	fi
}

For different older shell/bash versions you might need quotes around the regex.

Btw O’Reilly’s “Learning the Bash” is available within Google Books

Edit: another very important bookmark for bashscripting is the Advanced Bash-Scripting Guide

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shell command: translate

tolleiv — Tue, 28 Apr 2009 16:22:55 +0000

“Translate, squeeze, and/or delete characters from standard input,
writing to standard output.”

… that’s the manpage description of the shell-command I just found (with the help of a good friend) … and besides sed this is a very handy way to do simple string-operations on stdin.

He used it to replace (old) Mac newline characters with Unix newline charaters within files (as seen on wikipedia):
tr '\r' '\n' < old.file > new.file

Btw I still think that it’s stupid that users still have all the hazzle with newline charaters – why can’t the OS-developers just recognize all types of newlines?

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the subshell is your friend

tolleiv — Fri, 24 Apr 2009 21:10:29 +0000

Today I tried to find a way to track the time of a shell-command and to log that runtime into a file. I was already aware of the time command which is a bash build-in. Due to that it passes its output directly to the user without using either stdout or stderr and therefore there’s no “easy” way to redirect the output directly into a file.

But bash als provides subshells and in this case that’s how you can use the output (which is passed on stderr in this case).

(time sleep 5) 2> time.log

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… much better way to use your shell

tolleiv — Wed, 15 Apr 2009 19:22:38 +0000

Click here to view the embedded video.

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find the newest file within a folder….

tolleiv — Tue, 14 Apr 2009 20:14:42 +0000

These are two neat little commands to find the newest and oldest file within a folder and it’s subfolder:
find . -type f -printf "%T@ %p \n" | sort -n -k 1,1 | awk '{print $2}' | tail -n 1 find . -type f -printf "%T@ %p \n" | sort -n -k 1,1 | awk '{print $2}' | head -n 1
If you’d like to know how old/young these files are try these two:
find . -type f -printf "%T@ %C+ %p \n" | sort -n -k 1,1 | tail -n 1 find . -type f -printf "%T@ %C+ %p \n" | sort -n -k 1,1 | head -n 1

I hope that’s a good starter for the “blog”

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