using sed to replace just the first occurrence of a string

[steophy]

Hello there

Node version (or tell us if you're using electron or some other framework):

v7.10.0

ShellJS version (the most recent version/Github branch you see the bug on):

v0.8.0

Operating system:

MacOs HighSierra 10.13.2

Description of the bug:

I'm using shelljs to perform a sed command and replace the whole line with a certain occurrence with another text. Here's the code that I'm using:

require('shelljs/global');

var new_version = process.argv[2];

sed('-i', /^.*version.*$/,
    '  "version": "'+new_version+'",',
    'package.json');

That version works but it replaces all the occurrence of "version". I have tried this code to replace only the first occurrence:

sed('-i', '0,/^.*version.*$/',

but that's not working at all: the file remains unchanged.

What am I missing?

[nfischer]

shell.sed() doesn't change every match, it changes the first match per line (so this is working as intended). To demonstrate:

> shell.cat('file.txt');
hello world
hello hello world
> shell.sed(/hello/, 'bye', 'file.txt'); // first occurrence, for each line
bye world
bye hello world
> shell.sed(/hello/g, 'bye', 'file.txt'); // all occurrences, on all lines
bye world
bye bye world

---

To achieve what you want, you can try:

var contents = shell.cat('myfile');
var newContents = contents.replace(/(.|\n)*(my pattern)(.|\n)*/, 'replacement text');
(new ShellString(newContents)).to('myfile');

However, a more robust way to solve you specific problem would be:

var myPackage = require('package.json');
myPackage.version = 'new version number';
// pretty print with 2 space indent and trailing newline
var packageString = JSON.stringify(myPackage, null, 2) + '\n';
fs.writeFileSync('package.json', packageString);

[edgarechm]

Wait, wait.... so reading your last comment:

"To achieve what you want, you can try:

var contents = shell.cat('myfile');
var newContents = contents.replace(/(.|\n)(my pattern)(.|\n)/, 'replacement text');
(new ShellString(newContents)).to('myfile');"

Your solution to the issue is .... NOT USING "shell.sed" and use "contents.replace" instead? shell.sed doesn't work for this purpose?

[nfischer]

shell.sed doesn't work for this purpose?

shell.sed() will replace the first occurrence of a pattern, for each line of input. It behaves like unix sed. If you want to only replace the very first occurrence, String.prototype.replace is already perfect, no library necessary.

[Madsn]

So, nothing like this is supported?
https://stackoverflow.com/a/13438118/605449

[nfischer]

So, nothing like this is supported?
stackoverflow.com/a/13438118/605449

Currently, not supported (not opposed to it, however).

Also, that wouldn't necessarily be the right solution for the original post, but that shouldn't deter us from implementing it.