Comments on: Pathmunge http://involution.com/2006/05/11/pathmunge/ Tony Perrie's Weblog Tue, 15 May 2012 22:43:17 +0000 hourly 1 http://wordpress.org/?v=3.3.2 By: Tim Bingham http://involution.com/2006/05/11/pathmunge/comment-page-1/#comment-4165 Tim Bingham Fri, 01 Dec 2006 17:20:40 +0000 http://involution.com/2006/05/11/pathmunge/#comment-4165 The pathmunge() above dosen't work - it always adds its first argument to PATH, even if it is already present. The problem is in the argument to egrep which is quoted with single quotes so the $1 doesn't get expanded. This means that egrep doesn't search PATH for the first argument, instead it searches literally for '$1'. The fix is to use double quotes like this "(^|:)$1($|:)" instead of '(^|:)$1($|:)' Normally I wouldn't be such a pedant but this page is the top hit when googling for "pathmunge" :-) The pathmunge() above dosen’t work – it always adds its first argument to PATH, even if it is already present.

The problem is in the argument to egrep which is quoted with single quotes so the $1 doesn’t get expanded. This means that egrep doesn’t search PATH for the first argument, instead it searches literally for ‘$1′.

The fix is to use double quotes like this “(^|:)$1($|:)” instead of ‘(^|:)$1($|:)’

Normally I wouldn’t be such a pedant but this page is the top hit when googling for “pathmunge” :-)

]]> By: JTAxx http://involution.com/2006/05/11/pathmunge/comment-page-1/#comment-265 JTAxx Fri, 12 May 2006 18:43:49 +0000 http://involution.com/2006/05/11/pathmunge/#comment-265 NO! NO!

]]> By: Administrator http://involution.com/2006/05/11/pathmunge/comment-page-1/#comment-264 Administrator Fri, 12 May 2006 18:27:31 +0000 http://involution.com/2006/05/11/pathmunge/#comment-264 That's a pipe, man. Come on, get with the program... That’s a pipe, man. Come on, get with the program…

]]> By: JTAxx http://involution.com/2006/05/11/pathmunge/comment-page-1/#comment-263 JTAxx Fri, 12 May 2006 18:17:10 +0000 http://involution.com/2006/05/11/pathmunge/#comment-263 my question 2 was in regards to the first "|", but now i see that you pipe the echo to the egrep then the ! refers to the final output...life's hard without parenthese! my question 2 was in regards to the first “|”, but now i see that you pipe the echo to the egrep then the ! refers to the final output…life’s hard without parenthese!

]]> By: Administrator http://involution.com/2006/05/11/pathmunge/comment-page-1/#comment-262 Administrator Fri, 12 May 2006 16:53:16 +0000 http://involution.com/2006/05/11/pathmunge/#comment-262 All that pathmunge does is sets up a bash function to add directories to the beginning or at the end of your <code>$PATH</code> <p><b>Before</b>: <code>pathmunge ~/bin</code> would set <code>PATH=~/bin:$PATH</code> <b>After</b>: <code>pathmunge ~/bin after</code> would set <code>PATH=$PATH:~/bin</code></p> The egrep nonsense at the beginning is to make sure that the path doesn't already exist in your path (prevents you from adding it twice, aliases notwithstanding). The parentheses and | character in a regular expression is indeed a logical OR operation. E.g. (Jer|Ch)rome would match Jerome and Chrome. These operations fall into the realm of extended regular expressions which is why the author rightly called egrep. The $ and ^ in a regex means beginning of line and end of line. So, the egrep stuff is just a low rent way of parsing a colon delimited $PATH. If you add this function to your ~/.bashrc or /etc/bashrc, bash treats it as a command that can be invoked from the command-line. All that pathmunge does is sets up a bash function to add directories to the beginning or at the end of your $PATH

Before: pathmunge ~/bin would set PATH=~/bin:$PATH
After: pathmunge ~/bin after would set PATH=$PATH:~/bin

The egrep nonsense at the beginning is to make sure that the path doesn’t already exist in your path (prevents you from adding it twice, aliases notwithstanding). The parentheses and | character in a regular expression is indeed a logical OR operation. E.g. (Jer|Ch)rome would match Jerome and Chrome. These operations fall into the realm of extended regular expressions which is why the author rightly called egrep. The $ and ^ in a regex means beginning of line and end of line. So, the egrep stuff is just a low rent way of parsing a colon delimited $PATH. If you add this function to your ~/.bashrc or /etc/bashrc, bash treats it as a command that can be invoked from the command-line.

]]> By: Ali http://involution.com/2006/05/11/pathmunge/comment-page-1/#comment-259 Ali Fri, 12 May 2006 16:16:10 +0000 http://involution.com/2006/05/11/pathmunge/#comment-259 Yeah, I have no idea what you're talking about. Yeah, I have no idea what you’re talking about.

]]> By: JTAxx http://involution.com/2006/05/11/pathmunge/comment-page-1/#comment-258 JTAxx Fri, 12 May 2006 15:22:01 +0000 http://involution.com/2006/05/11/pathmunge/#comment-258 1. what does ! echo $PATH do? 2. does "|" == "OR" 3. i can't tell how this updates your profile. 1. what does ! echo $PATH do?
2. does “|” == “OR”
3. i can’t tell how this updates your profile.

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