String Operations

${#var} returns the number of characters (not bytes) in the value of variable var as an integer. When the locale is set to UTF-8, multibyte characters are each counted as one character.

${var:offset:length} extracts length characters starting at position offset (0-based) and returns the result. If length is omitted, it returns everything from offset to the end of the string. A negative offset counts from the end, but because it can be confused with the :- default-value expansion, it is recommended to write ${var: -3} (with a space after the colon) or ${var:$(( ${#var} - 3 ))}.

${var/old/new} replaces the first match of pattern old (glob patterns are supported) with new and returns the result. Using // replaces all matches. Omitting new (i.e., ${var/old/}) deletes the matched portion.

Pattern stripping returns the value of a variable with a matching prefix or suffix removed. It is commonly used to strip the directory part or file extension from a path. # / % use the shortest match, while ## / %% use the longest match.

The following table shows parameter expansion equivalents for basename and dirname as path manipulation examples.

Bash 4.0 and later support case conversion using ^^ and ,,. These are not available in the default bash on macOS (version 3.2), so use the tr command as an alternative when running on macOS.

yakuza_string.sh

#!/bin/bash
# -----------------------------------------------
#  Demonstrates string operations (length, extraction,
#  substitution, stripping) using Yakuza series characters
# -----------------------------------------------

# -----------------------------------------------
#  1. String length (${#var})
# -----------------------------------------------

name1="桐生一馬"
name2="真島吾朗"
name3="冴島大河"
name4="秋山駿"
name5="堂島大吾"

echo "=== 1. String length ==="

# Use ${#var} to get the character count of a variable
echo "${name1} length: ${#name1}"   # → 4
echo "${name2} length: ${#name2}"   # → 4
echo "${name3} length: ${#name3}"   # → 4
echo "${name4} length: ${#name4}"   # → 3
echo "${name5} length: ${#name5}"   # → 4

echo ""

# -----------------------------------------------
#  2. Substring extraction (${var:offset:length})
# -----------------------------------------------

echo "=== 2. Substring extraction ==="

title="東城会四代目会長・桐生一馬"

# offset=0, length=5 → extract 5 characters from the start
echo "Title: ${title:0:5}"           # → 東城会四代

# offset=6 → extract from position 6 to the end
echo "Name part: ${title:6}"          # → 桐生一馬

# Extract the last 2 characters (a space after the colon is required)
echo "Last 2 chars: ${title: -2}"       # → 一馬

echo ""

# -----------------------------------------------
#  3. Substitution (${var/old/new})
# -----------------------------------------------

echo "=== 3. Substitution ==="

org="東城会"

# Replace only the first match
sentence="桐生一馬は東城会の幹部だ。東城会は神室町を拠点とする。"
echo "Single replace: ${sentence/東城会/近江連合}"
# → 桐生一馬は近江連合の幹部だ。東城会は神室町を拠点とする。

# Use // to replace all occurrences
echo "Replace all:    ${sentence//東城会/近江連合}"
# → 桐生一馬は近江連合の幹部だ。近江連合は神室町を拠点とする。

# Omitting new deletes the matched part
echo "Delete:         ${sentence/東城会/}"
# → 桐生一馬はの幹部だ。東城会は神室町を拠点とする。

# Anchor-at-start substitution (#) to prepend a title
name="桐生一馬"
echo "Prefix match:   ${name/#桐生/東城会四代目・桐生}"
# → 東城会四代目・桐生一馬

echo ""

# -----------------------------------------------
#  4. Pattern stripping (${var#pattern} / ${var%pattern})
# -----------------------------------------------

echo "=== 4. Pattern stripping ==="

filepath="/home/yakuza/save/kiryu_chapter5.dat"

# Remove longest prefix up to the last / → get filename only
filename="${filepath##*/}"
echo "Filename:    ${filename}"         # → kiryu_chapter5.dat

# Remove shortest suffix from last . → strip extension
basename_noext="${filename%.*}"
echo "No extension: ${basename_noext}"   # → kiryu_chapter5

# Remove longest prefix up to last . → get extension only
ext="${filename##*.}"
echo "Extension:   ${ext}"              # → dat

# Remove shortest suffix from last / → get directory part
dirpath="${filepath%/*}"
echo "Directory:   ${dirpath}"        # → /home/yakuza/save

echo ""

# -----------------------------------------------
#  5. Combined example — format a character record
# -----------------------------------------------

echo "=== 5. Combined example ==="

# Assume a record is stored in "title_name" format
record="四代目会長_桐生一馬"

# Extract the part before _ (title)
role="${record%%_*}"
echo "Title: ${role}"                   # → 四代目会長

# Extract the part after _ (name)
fullname="${record##*_}"
echo "Name:  ${fullname}"               # → 桐生一馬

# Display the character count of the name
echo "Name length: ${#fullname}"       # → 4

# Extract the family name (first 2 characters)
family="${fullname:0:2}"
echo "Family name: ${family}"                   # → 桐生

$ chmod +x yakuza_string.sh
$ ./yakuza_string.sh
=== 1. String length ===
桐生一馬 length: 4
真島吾朗 length: 4
冴島大河 length: 4
秋山駿 length: 3
堂島大吾 length: 4

=== 2. Substring extraction ===
Title: 東城会四代
Name part: 桐生一馬
Last 2 chars: 一馬

=== 3. Substitution ===
Single replace: 桐生一馬は近江連合の幹部だ。東城会は神室町を拠点とする。
Replace all:    桐生一馬は近江連合の幹部だ。近江連合は神室町を拠点とする。
Delete:         桐生一馬はの幹部だ。東城会は神室町を拠点とする。
Prefix match:   東城会四代目・桐生一馬

=== 4. Pattern stripping ===
Filename:    kiryu_chapter5.dat
No extension: kiryu_chapter5
Extension:   dat
Directory:   /home/yakuza/save

=== 5. Combined example ===
Title: 四代目会長
Name:  桐生一馬
Name length: 4
Family name: 桐生

Shell script string operations can be completed entirely within the shell by combining parameter expansion symbols, without relying on external commands. Use ${#var} to get the string length, ${var:offset:length} to extract a substring from any position, and ${var/old/new} with ${var//old/new} for single and global substitution. To strip patterns from the beginning, use ${var#pattern} (shortest) or ${var##pattern} (longest); to strip from the end, use ${var%pattern} (shortest) or ${var%%pattern} (longest). For path manipulation in particular, remembering three forms — ${path##*/} (get filename), ${path%/*} (get directory), and ${file%.*} (strip extension) — means you can avoid calling basename or dirname. For the basics of declaring and referencing variables, see also Variable assignment, referencing, and scope.