Editing few lines of a file in bash

Question

Hello I would like to parse a js file in bash containing settings in this way :

user_pref("network.proxy.socks", "127.0.0.1");
user_pref("network.proxy.socks_port", 9150);
user_pref("network.proxy.type", 1);

if the lines do not exist, it should be created (>>append).
if the lines are already set with those values : do nothing.
If the lines are already set with different values, change it for values "127.0.0.1", 9150, 1

So far I can perform point 1 and 2, but I struggle on point 3. I believe it can be achieved by using bash conditionals, and 'sed' with a regex pattern. Can anyone (regex guru) help me please ?

Quick introduction to my problem :

I am writing a bash script on OS X and have socks5 listening on 127.0.0.1:9150. I want then to set those settings for Firefox by editing the prefs.js file (equivalent of url about:config). The GUI for this is Preferences/Advanced/Network/Connection Settings/Manual Proxy/Socks5.

FYI, here's my script, the missing part is ###MISSING PART### :

function sshD
{
    pkill firefox #Kill existing instance(s) of Firefox
    #Create HTTP Proxy via SSH Tunnel
    ssh -Cc blowfish -D9150 -Nf myuser@mydomain
    fxpref="$HOME/Library/Application Support/Firefox/Profiles/"; fxpref="$fxpref`ls "$fxpref" | awk 'NR==1'`/prefs.js"
    test ! -f "$fxpref".backup && cp "$fxpref" "$fxpref".backup
    proxypref=`cat "$fxpref" | grep proxy`
    ###MISSING PART###
    /Applications/Firefox.app/Contents/MacOS/firefox-bin -private > /dev/null 2>&1 &
}

why can't you over write with the default values always with out performing any check? — Suku, Jul 01 '14 at 11:09
Because this is point 3, I do not .know how to detect the line and replace it with sed. If I >>append, I end up creating duplicates. — Florian Bidabé, Jul 01 '14 at 11:33

score 4 · Accepted Answer · edited May 23 '17 at 12:05

A solution that works with FreeBSD sed (OS X) as well as with GNU sed (Linux) - basics of the approach are based on @anishsane's answer:

Note:

The assumption is that it's OK to not preserve the original order of preferences in the input file so as to simplify the solution.
Thus, this solution effectively first removes existing preferences of interest (if any) from the input file, and then appends them with the desired (new) values to the end.

sed -En '/user_pref\("network\.proxy\.(socks|socks_port|type)"/!p
        $ a\
user_pref("network.proxy.socks", "127.0.0.1");\
user_pref("network.proxy.socks_port", 9150);\
user_pref("network.proxy.type", 1);
        ' prefs.js

Note: The above just outputs the result to stdout; if you wanted to replace the input file with the result, saving the original to *.backup, use:

sed -En -i'.backup' ...

Explanation:

-E turns on support for extended regular expressions, which adds crucial features such as | for alternation (aside from needing less escaping).
-n suppresses default output of (potentially modified) input lines, so that only explicit output functions such as p, a, and i produce output.
/user_pref\("network\.proxy\.(socks|socks_port|type)"/!p causes all lines NOT containing the preferences of interest to be printed; in other words: existing lines containing the preferences of interest (with their current values) are effectively deleted.
$ a appends text to the output after the last line ($) of input, and here simply outputs the preferences of interest with the desired new values.
Overall, the \-escaped newlines are carefully placed to make FreeBSD sed happy - a pure GNU sed solution would be simpler; see https://stackoverflow.com/a/24276470/45375 for the differences between the two implementations.

It is now working as expected thank you very much.Very good to know how to use sed on BSD, thank you again ! — Florian Bidabé, Jul 02 '14 at 10:23

anishsane · Answer 2 · 2014-07-01T12:49:23.307

1

I believe that firefox's pref.js is read line-by-line & the sequence of these preferences is not important.

So, this should work:

sed '/user_pref("network.proxy.\(socks\|socks_port\|type\)"/d;
        $auser_pref("network.proxy.socks", "127.0.0.1");\nuser_pref("network.proxy.socks_port", 9150);\nuser_pref("network.proxy.type", 1);' pref.js

edited Jul 01 '14 at 12:49

answered Jul 01 '14 at 11:19

anishsane

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Thank you anishsane, however the option -r does not exists on "Darwin Kernel Version 13.1.0" (OS X 10.9). man sed -> HISTORY : A sed command, written by L. E. McMahon, appeared in Version 7 AT&T UNIX. BSD May 10, 2005 – Florian Bidabé Jul 01 '14 at 11:40
I had added `-r` only to bypass some escaping of `(`, `|` with `\`... Misusing features for own laziness ;) Updated the answer. – anishsane Jul 01 '14 at 12:49
On OSX you can use `-E` instead of `-r` (to enable support for _extended_ regexes) (note that `-E` even works with GNU `sed`, though the manual doesn't say so). However: Alternation (`|`) in a _basic_ regex is not part of POSIX, so FreeBSD `sed` only supports alternation with `-E`. There are other things FreeBSD/OSX `sed` doesn't support, such as appending text directly to the `a` function and using `\n` in the text argument - see http://stackoverflow.com/a/24276470/45375 – mklement0 Jul 01 '14 at 13:08
Thanks I did indeed have a "error: parentheses not balanced", but I now get a "sed: 1: "/user_pref("network.pro ...": command a expects \ followed by text". I'm sorry if I'n missing something essential. – Florian Bidabé Jul 01 '14 at 13:28
FreeBSD/OSX ... OpenBSD/OSX(e.g. pfctl)... Linux...I thought using bash would kind of work both ways for unix/linux kernels/flavours, guess I'm not a developer fella. – Florian Bidabé Jul 01 '14 at 13:35
^^ `bash` & `sed` are independent :-) – anishsane Jul 01 '14 at 13:47
`bash` is not in the mix here - only the differing `sed` implementations - there are, sadly, many small differences, which I've attempted to summarize in the linked answer. @FlorianBidabe: The short of it: follow `a` with `\ ` (ignore the space after - needed it for formatting) followed by an _actual_ newline; similarly, replace the `\n` instances with `\ ` followed by an _actual_ newline. (Alternatively, splice `$'\n'` into the string to create newlines). – mklement0 Jul 01 '14 at 13:49
Elegant solution - if you fix it to work on OSX, I'll up-vote. – mklement0 Jul 01 '14 at 14:00
Right, thanks for your help, I get that the shell(command line interpreter) has nothing to do with a unix utility like sed. You guys are more knowledgeable than I in terms of scripting, if we avoid using sed, since there are different implementations, Can we use something else ? I know vim but this requires manual input, right ? – Florian Bidabé Jul 01 '14 at 14:01
<> Guess I'm gonna spend an over sleepless night on this ahah – Florian Bidabé Jul 01 '14 at 14:02
On 2nd thought: even with GNU `sed` your answer will only work if the last input line does not match the regex, because the `d` will otherwise prevent the `$a` from getting executed. – mklement0 Jul 01 '14 at 14:28
1

^^ That's actually right. Even heuristically, the second time when the script runs, these entries will be at the end. But looks like your answer already has that covered. – anishsane Jul 02 '14 at 05:58

Editing few lines of a file in bash

2 Answers2