Motivation

xseq attempts to be an extended form of the seq command from coreutils. While seq mostly works with numbers, xseq can iterate over ranges of letters. Some of seq's features are available in xseq.

Goal: More flexible iteration

• seq is great. It can be used in bash scripts as an easy way to iterate over a range of numbers:

for num in $(seq 1 100); do
    echo "Fetching record ${num}..."
    curl -sSL "https://api.foobar.dev/api/v1/user/${num}" > ./users/"${num}.json"
done

• But sometimes, it would be nice to have the same iteration over a range of letters:

for LETTER $(xseq A Z); do
    echo "Fetching users starting with letter: ${LETTER}..."
    curl -sSL "https://api.foobar.dev/api/v1/user?name_starts_with=${LETTER}" > ./users-"${LETTER}".json
done

Being woefully unsatisfied with invoking a scripting engine, I decided I'd just implement the features seq doesn't have.

Usage

Usage: xseq [OPTION]... <LAST>
 or:   xseq [OPTION]... <FIRST> <LAST>
 or:   xseq [OPTION]... <FIRST> <INCREMENT> <LAST>
Print numbers or letters from FIRST to LAST, in steps of INCREMENT.

  -a, --alpha       Treat FIRST and LAST as letters.
  -z, --zero        When LAST is the only argument, assume FIRST is zero
  -s, --separator=STRING   use STRING to separate numbers (default: \n)
  -h, --help        display this help and exit
  -v, --version     output version information and exit

 <INCREMENT> Works for both numbers and letters (when -a)

  If FIRST and LAST are letters, the range will be interpretted as if -a (or --alpha) was passed as an argument
  As a result, the following examples are all equivalent:
   xseq -a A Z
   xseq A Z
 When FIRST and LAST are letters, INCREMENT can be used without explicitly specifying -a or --alpha.
 The following invocation will skip print every 3rd letter between A and Z:
   xseq A 3 Z

Looping over numbers

• This is exactly like seq

$ xseq 1 5
1
2
3
4
5

Letters are just integers

$ xseq A F
A
B
C
D
E
F

<INCREMENT> parameter

• Useful for printing every N letters/numbers

$ xseq A 3 M
A
D
G
J
M

Ascending vs Descending

• if <FIRST> is greater than <LAST>, the generated sequence counts down

$ xseq Z T
Z
Y
X
W
V
U
T

Descending with <INCREMENT>

$ xseq Z 3 T
Z
W
T
$

Support for -s STRING and --separator=STRING

$ xseq -s , 0 10
0,1,2,3,4,5,6,7,8,9,10,$

$ xseq --separator='}{' 0 10
0}{1}{2}{3}{4}{5}{6}{7}{8}{9}{10}{$

• Admittedly, this output is a bit janky, but you get the idea.
• By default, STRING is the newline character. There currently is no support for windows newline sequences of \r\n

Minor improvements

• xseq automatically shows you the help screen if you pass it no parameters.
• It also shows the help screen if you pass -h. The original seq required the user to run seq --help, which is self-documenting, but tedious for the user

Features from seq

• We plan on porting --format=FMT
• We have no plans to port --equal-width

Building

You will need to have g++ installed. A simple make will build the binary for you. The code was written using widely supported C++ features. The code should compile just fine without having to tell your compiler which version of the c++ standard to use. Everything is written using well-established libraries. There are only three header files included.

License

• Copyright (C) 2025 William Merfalen
• License is GPLv3+
• This is free software: you are free to change and redistribute it.
• There is NO WARRANTY, to the extent permitted by law.
• This code is inspired by, but contains ABSOLUTELY NO code from coreutils' version of seq

Special thanks

• Ulrich Drepper Is the original author of seq