Replace all instances of a string in a file

iicapn · 02-12-2021, 06:23 PM

I'm trying to script a hostname change... for instance in my /etc/hosts file, I have a line that says:

Code:

127.0.1.1	debian10.mydomain.com	debian10

If I run the following on the command line, it shows me what I want:

Code:

sed 's|debian10|mybox|g' /etc/hosts

But it doesn't replace my /etc/hosts file... it just shows me the changes.

adding ` > /etc/hosts` to the end doesn't seem to help. Is this the best way to replace a string in a file?

Many thanks in advance :-)

syg00 · 02-12-2021, 06:34 PM

When in doubt read the manpage.

iicapn · 02-12-2021, 06:38 PM

Quote:

Originally Posted by syg00

When in doubt read the manpage.

You are right, thank you. `-i` does the trick. DUH!

Turbocapitalist · 02-12-2021, 11:45 PM

Also remember that -i can take a parameter to append to the backup file. Without any option, it will just overwrite the file without keeping a backup. For example,

Code:

sed -i.orig 's|debian10|mybox|g' /etc/hosts

syg00 · 02-13-2021, 04:15 AM

Lots of comments bemoan the manpages - I use them as the first reference always. Then "info" in need.
Mind you, some could do with polish for clarity - need I mention "man find" ?.

MadeInGermany · 02-13-2021, 07:23 AM

Always be as precise as possible!
A step to more precision is

Code:

sed -i.orig 's|\<debian10\>|mybox|g' /etc/hosts

Now debian10 is substituted but not debian100
Recent GNU Linux also takes (incorporated from PCRE)

Code:

sed -i.orig 's|\bdebian10\b|mybox|g' /etc/hosts

In case /etc/hosts is a link (true on Solaris but not yet Linux), a copy changes the data but leaves the inode (the linkage, the owner, the permissions) intact

Code:

cp -p /etc/hosts /etc/hosts.bak && sed 's|\<debian10\>|mybox|g' /etc/hosts.bak > /etc/hosts

The sed -i takes care about owner and permissions as well - but breaks the link.

shruggy · 02-13-2021, 09:24 AM

While perhaps not directly applicable to the question at hand, I prefer using specialized tools wherever possible.

Code:

$ hostctl -h

hostctl is a CLI tool to manage your hosts file with ease.
You can have multiple profiles, enable/disable exactly what
you need each time with a simple interface.

Usage:
  hostctl [command]

Available Commands:
  add         Add content to a profile in your hosts file.
  backup      Creates a backup copy of your hosts file
  disable     Disable a profile from your hosts file.
  enable      Enable a profile on your hosts file.
  help        Help about any command
  list        Shows a detailed list of profiles on your hosts file.
  remove      Remove a profile from your hosts file.
  replace     Replace content to a profile in your hosts file.
  restore     Restore hosts file content from a backup file.
  status      Shows a list of profile names and statuses on your hosts file.
  sync        Sync some system IPs with a profile.
  toggle      Change status of a profile on your hosts file.

Flags:
  -c, --column strings     Column names to show on lists. comma separated
  -h, --help               help for hostctl
      --host-file string   Hosts file path (default "/etc/hosts")
      --no-color           force colorless output
  -o, --out string         Output type (table|raw|markdown|json) (default "table")
  -q, --quiet              Run command without output
      --raw                Output without borders (same as -o raw)
  -v, --version            version for hostctl

Use "hostctl [command] --help" for more information about a command.

Code:

$ hostess -h
An idempotent tool for managing /etc/hosts

Commands

    fmt                  Reformat the hosts file

    add <hostname> <ip>  Add or overwrite a hosts entry
    rm <hostname>        Remote a hosts entry
    on <hostname>        Enable a hosts entry
    off <hostname>       Disable a hosts entry

    ls                   List hosts entries
    has                  Exit 0 if entry present in hosts file, 1 if not

    dump                 Export hosts entries as JSON
    apply                Import hosts entries from JSON

    All commands that change the hosts file will implicitly reformat it.

Flags

    -n will preview changes but not rewrite your hosts file

Configuration

    HOSTESS_FMT may be set to unix or windows to force that platform's syntax
    HOSTESS_PATH may be set to point to a file other than the platform default

About

    Copyright 2015-2020 Chris Bednarski <chris@cbednarski.com>; MIT Licensed
    Portions Copyright the Go authors, licensed under BSD-style license
    Bugs and updates via https://github.com/cbednarski/hostess

Found them both via this list.

Brains · 02-13-2021, 05:21 PM

Same here, here's one I like:

Quote:

hostnamectl set-hostname willy