sed

sed is a shell scripting and stream-processing language first appearing in 1974.

Hello World

#!/bin/sed -f

# BEGIN_FRAGLET
1s/^/Hello World!/
# END_FRAGLET

Coding Guide

Language Version

GNU sed (stream editor)

Execution Model

• Stream editor that processes text line by line
• Reads from stdin or files
• Applies commands to each line (or specified lines)
• Outputs modified text to stdout

Key Characteristics

• Line-oriented processing
• Commands operate on pattern space (current line)
• Addresses specify which lines to process (line numbers, regex patterns)
• Commands: s (substitute), p (print), d (delete), a (append), i (insert), etc.
• Flags: g (global), p (print), i (case-insensitive)
• Delimiters: / is standard, but any character can be used
• Case-sensitive pattern matching (unless using i flag)

Fragment Authoring

Write valid sed commands. Your fragment becomes the script body. Your fragment will execute as part of the sed script.

Important: sed processes input line by line. If your fragment needs to process multiple lines, you may need to use the hold space or multi-line commands.

Available Commands

Standard sed commands are available:

• s/pattern/replacement/flags - Substitute pattern with replacement
• p - Print the pattern space
• d - Delete the pattern space
• a\text - Append text after the current line
• i\text - Insert text before the current line
• c\text - Change/replace the current line
• y/src/dst/ - Transliterate characters
• q - Quit processing
• = - Print line number
• r file - Read file and append to output
• w file - Write pattern space to file

Common Patterns

• Substitute: s/old/new/ or s/old/new/g (global)
• Print: p (usually with -n flag to suppress default output)
• Delete: d
• Append: a\Text to append
• Insert: i\Text to insert
• Address ranges: 1,5s/old/new/ (lines 1-5), /pattern/s/old/new/ (matching lines)
• Multiple commands: s/old/new/; s/foo/bar/ or -e 's/old/new/' -e 's/foo/bar/'
• Conditional: /pattern/{ s/old/new/; p; }

Examples

# Simple output
1s/^/Hello from fragment!/

# Multiple substitutions
1s/^/Hello /; 1s/$/ World!/

# Print with line numbers
=; p

# Append text
a\This is appended text

# Insert text
i\This is inserted text

# Substitute with case-insensitive flag
s/hello/HELLO/gi

# Process specific lines
1,3s/old/new/g

# Pattern-based substitution
/pattern/s/old/new/

# Multiple commands on same line
1s/^/Prefix /; 1s/$/ Suffix/

# Delete and substitute
1d; 2s/old/new/

# Conditional processing
/error/{ s/error/ERROR/; p; }

# Creative formatting: Transform a list into a formatted output
1s/^/Colors: /; 2s/^/  * /; 3s/^/  * /; 3s/$/ (favorite)/

Caveats

• sed processes one line at a time by default
• Pattern space contains the current line
• Hold space can store data between lines (advanced)
• Addresses are line numbers or regex patterns
• Commands are separated by ; or newlines
• Use -n flag with p command to avoid duplicate output
• Delimiters can be any character: s|old|new| works the same as s/old/new/
• Special characters in patterns need escaping: \., \*, \+, etc.
• Replacement text can reference matched groups: s/\(.*\)/\1/
• Multi-line operations require special handling (hold space, N command)

Fraglet Scripts

Echo Args

#!/usr/bin/env -S fragletc --vein=sed
1s/^/Args: /

Stdin Upper

#!/usr/bin/env -S fragletc --vein=sed
y/abcdefghijklmnopqrstuvwxyz/ABCDEFGHIJKLMNOPQRSTUVWXYZ/

Test

#!/usr/bin/env -S fragletc --vein=sed
1s/^/Hello World!/

Connections

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