Sed (Stream Editor) adalah text processing utility yang powerful untuk melakukan basic transformations pada input stream. Meski tidak se-powerful AWK untuk complex processing, Sed unggul dalam text substitution dan manipulation.

1. Sintaks Dasar Sed

Struktur Command

sed [options] 'command' file
sed [options] -e 'command1' -e 'command2' file

Command Fundamental

# Print semua baris (default behavior)
sed '' file.txt
sed -n 'p' file.txt
Print baris tertentu
sed -n '5p' file.txt        # Line 5
sed -n '5,10p' file.txt     # Lines 5-10
sed -n '$p' file.txt        # Last line
sed -n '1~2p' file.txt      # Every 2nd line starting from 1
Print multiple ranges
sed -n '1p;5p;10p' file.txt

2. Substitution dengan Sed

Basic Substitution

# Replace text (hanya first occurrence per line)
sed 's/old/new/' file.txt
Replace all occurrences dalam line (global)
sed 's/old/new/g' file.txt
Replace specific occurrence
sed 's/old/new/2' file.txt    # Replace 2nd occurrence
sed 's/old/new/2g' file.txt   # Replace 2nd dan seterusnya
Use different delimiters (useful untuk paths)
sed 's|/usr/local|/opt|g' file.txt
sed 's#/home/user#/data#g' file.txt
sed 's_old_new_g' file.txt

Advanced Substitution

# Case insensitive
sed 's/old/new/gi' file.txt
Only print modified lines
sed -n 's/old/new/gp' file.txt
Capture groups dengan backreferences
sed 's/(.
):(.)/\2: \1/' file.txt
Replace dengan line number
sed = file.txt | sed 'N; s/\n/ /'
Replace dengan environment variable
sed "s/USER/$USER/g" file.txt
Replace only specific lines
sed '5s/old/new/' file.txt      # Line 5 only
sed '/pattern/s/old/new/' file.txt  # Lines matching pattern
sed '1,10s/old/new/' file.txt   # Lines 1-10

3. Deletion dan Insertion

Deleting Lines

# Delete baris tertentu
sed '5d' file.txt             # Delete line 5
sed '5,10d' file.txt          # Delete lines 5-10
sed '$d' file.txt             # Delete last line
sed '1d' file.txt             # Delete first line
Delete based on pattern
sed '/pattern/d' file.txt     # Delete lines with pattern
sed '/pattern/!d' file.txt    # Delete lines NOT matching pattern
Delete blank lines
sed '/^$/d' file.txt
sed '/^[[:space:]]*$/d' file.txt
Delete lines dengan whitespace only
sed '/^[[:space:]]*$/d' file.txt

Inserting dan Appending

# Insert before line
sed '5i\This is new line' file.txt
Append after line
sed '5a\This is appended' file.txt
Insert multiple lines
sed '5i\
Line 1\
Line 2\
Line 3' file.txt
Append after last line
sed '$a\This is last' file.txt
Insert at beginning of file
sed '1i# Header' file.txt

4. Addressing dan Ranges

Line Addressing

# Single line
sed '5s/old/new/' file.txt
Line range
sed '5,10s/old/new/' file.txt
From line to end
sed '5,$s/old/new/' file.txt
Pattern matching
sed '/start/,/end/s/old/new/' file.txt
Regex pattern
sed '/^#/s/old/new/' file.txt
Multiple addresses
sed -e '1s/^/START/' -e '$s/$/END/' file.txt

Range Operations

# Process range
sed -n '/START/,/END/p' file.txt
Delete range
sed '/START/,/END/d' file.txt
Substitute dalam range
sed '/START/,/END/s/foo/bar/' file.txt

5. Advanced Sed Techniques

Multiple Commands

# Multiple sed commands
sed -e 's/foo/bar/' -e 's/baz/qux/' file.txt
Command file
sed -f commands.sed file.txt
Commands dalam file commands.sed:
s/foo/bar/
s/baz/qux/
5d

In-place Editing

# Edit file in-place (backup original)
sed -i.bak 's/foo/bar/g' file.txt
Edit file in-place tanpa backup
sed -i 's/foo/bar/g' file.txt
Edit multiple files
sed -i 's/foo/bar/g' *.txt

Working dengan Multiple Lines

# Print next line juga
sed -n '/pattern/{N;p}' file.txt
Join lines
sed ':a;N;$!ba;s/\n/ /g' file.txt
Delete newlines
sed ':a;N;$!ba;s/\n//g' file.txt
Merge every 2 lines
sed 'N;s/\n/ /' file.txt
Swap line order
sed 'n;G;h;P;d' file.txt

Case Conversion

# Convert ke uppercase
sed 's/.*/\U&/' file.txt
Convert ke lowercase
sed 's/.*/\L&/' file.txt
Capitalize first letter
sed 's/.*/\u&/' file.txt
Title case (setiap word)
sed 's/\b([a-z])/\u\1/g' file.txt

6. Praktis One-Liners

File Manipulation

# Remove comments dan blank lines
sed '/^[[:space:]]*#/d; /^[[:space:]]*$/d' config.conf
Add line numbers
sed = file.txt | sed 'N; s/\n/ /'
Double space file
sed G file.txt
Reverse lines of file
sed '1!G;h;$!d' file.txt
Remove trailing whitespace
sed 's/[[:space:]]*$//' file.txt
Remove leading whitespace
sed 's/^[[:space:]]*//' file.txt
Remove both leading dan trailing
sed 's/^[[:space:]]
//;s/[[:space:]]$//' file.txt
Indent each line dengan 4 spaces
sed 's/^/    /' file.txt

Data Processing

# Convert spaces ke tabs
sed 's/  */ /g' file.txt
Convert tabs ke spaces
sed 's/ /    /g' file.txt
Remove ANSI color codes
sed 's/\x1B[[0-9;]*[JKmsu]//g' file.txt
URL encode
sed 's/ /%20/g' file.txt
Wrap long lines at 80 characters
sed -n -e ':a' -e 's/^(.{80})/\1\/;ta' -e 'p' file.txt

Configuration File Editing

# Uncomment line
sed -i 's/^#Port 22/Port 22/' /etc/ssh/sshd_config
Change value
sed -i 's/^Port 22/Port 2222/' /etc/ssh/sshd_config
Add setting if not exists
sed -i '/^#*Port 22/!a\Port 2222' /etc/ssh/sshd_config
Delete setting
sed -i '/^PermitRootLogin yes/d' /etc/ssh/sshd_config
Replace dalam tag HTML
sed 's/<[^>]*>//g' file.html

Kesimpulan

Sed adalah tools yang sangat powerful untuk text transformation. Meski learning curve sedikit curam, menguasai Sed akan menghemat banyak waktu dalam text processing tasks.

Kapan Menggunakan Sed vs AWK:
– Sed: Simple text substitution, deletion, insertion
– AWK: Field-based processing, calculations, complex logic
– Both: Often used together dalam pipelines

Tips:
1. Selalu test dengan -n dan p sebelum in-place editing
2. Gunakan backup (-i.bak) untuk file penting
3. Kombinasikan dengan pipes untuk workflow complex
4. Gunakan command files untuk scripts panjang

Alternatives:
– tr: Simple character translation
– cut: Field extraction sederhana
– perl -pe: Perl one-liners (more powerful)
– awk: Field-based processing