= Ed =

'''`ed(1)`''' is a non-visual text editor. It remains a powerful utility for scripted in-place file manipulation.

<<TableOfContents>>

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== Installation ==

Most modern systems do not offer `ed(1)`. Instead `ex(1)`, which is bundled within the `vim` package, is symlinked to `ed(1)`. This will be pre-installed on any [[Linux]] or [[BSD]] operating system, as a POSIX utility.

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== Input Mode ==

`ed(1)` enters '''input mode''' after one the following commands has been given:

 * append (`a`)
 * change (`c`)
 * insert (`i`)

Exit input mode by giving a period (`.`) alone.

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== Examples ==

=== Insert a Line into a File ===

Shell scripts make it trivial to append to a file. There are excellent tools such as [[Sed|sed(1)]] for search/replacing text. But there isn't a trivial way to, for example, insert a new line of text into the Nth line of a file.

This script demonstrates how such a task could be automated in part.

{{{
# Inserts a new third line into the file,
# which sets `someYamlProperty` to `true` in a Markdown header of some file.
ed "$1" <<EOF
3i
someYamlProperty: true
.
w
EOF
}}}



=== Line Editing ===

This script will rewrite itself to echo a new message.

{{{
message=

#This function uses a heredoc to pass commands into `ed`.
#It works like this:
#  - `1c` targets the first line for changing. Everything entered in input mode will replace this line.
#  - `message="$1"` is being inserted. Note that shell variables are evaluated in a heredoc.
#  - `.` exits input mode
#  - `w` writes the edited file to disk
edScript() {
  ed -s "$(realpath -s $0)" <<EOF
1c
message="$1"
.
w
EOF
}

#If this script is given an arguments, the first argument is passed to the above function.
#Otherwise, the script just echoes "$message".
if [ $# -ge 1 ]; then
  edScript "$1"
else
  echo "$message"
fi

}}}

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== See also ==

[[https://www.gnu.org/software/ed/manual/ed_manual.html|GNU Ed manual]]

[[https://docs.freebsd.org/44doc/usd/10.exref/paper.pdf|Ex Reference Manual]], the BSD4.4 UNIX User's Supplementary Document (USD)

[[https://man.archlinux.org/man/ed.1|ed(1)]]

[[https://man.archlinux.org/man/ed.1p|ed(1p)]]

[[Sed|sed]]



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