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abbazs
abbazs

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A One-Liner `sed` Command to Format SSH Config File

#sed #ssh #formatting

SED Command 

sed -i -e '/^\s*#/!{/^\s*Host /!s/^\s*/\t/}' \
    -e '/^\s*Host /s/^\s*//' \
    ~/.ssh/config
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With backup of old config file having extension .old 

sed -i.old -e '/^\s*#/!{/^\s*Host /!s/^\s*/\t/}' \
    -e '/^\s*Host /s/^\s*//' \
    ~/.ssh/config
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Breakdown

  • Skip Commented Lines:
    • Ignores lines starting with #, possibly preceded by whitespace. 
  /^\s*#/!{}
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  • Indent Non-Host and Non-Comment Lines: 
  {/^\s*Host /!s/^\s*/\t/}
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  • Matches lines that do not start with Host. 
  /^\s*Host /!
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  • Replaces leading spaces or tabs with a single tab. 
  s/^\s*/\t/
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  • Remove Leading Spaces from Host Lines: 
  -e '/^\s*Host /s/^\s*//'
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  • Matches lines that start with Host. 
  /^\s*Host /
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  • Removes all leading spaces or tabs from those lines. 
  s/^\s*//
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Example

Input: 

Host myserver
HostName ssh.example.com
User myuser
 Port 22
 IdentityFile ~/.ssh/mykey

   Host another-server
    HostName another.example.com
   User anotheruser
Port 2022
IdentityFile ~/.ssh/anotherkey
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Output: 

Host myserver
    HostName ssh.example.com
    User myuser
    Port 22
    IdentityFile ~/.ssh/mykey

Host another-server
    HostName another.example.com
    User anotheruser
    Port 2022
    IdentityFile ~/.ssh/anotherkey
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This formats the file in place (-i flag), ensuring consistent indentation and removing leading spaces.

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