Setw and setfill equivalent in BASH

Question

Could you please tell me what the equivalent BASH code for the following C++ snippet would be:

std::cout << std::setfill('x') << std::setw(7) << 250;

The output is:

xxxx250

Thanks for the help!

Answer 1

If you're on Linux, it has a printf program for just this purpose. Other UNIX variants may also have it.

Padding a numeric with x is not really on of its use cases but you could get the same result with:

pax> printf "%7d\n" 250 | tr ' ' 'x'
xxxx250

That outputs the 250 with space padding, then uses the tr translate utility to turn those spaces into x characters.

If you're looking for a bash-only solution, you can start with:

pax> n=250 ; echo ${n}
250

pax> n=xxxxxxx${n} ; echo ${n}
xxxxxxx250

pax> n=${n: -7} ; echo ${n}
xxxx250

---

If you want a generalised solution, you can use this function fmt, unit test code is included:

#!/bin/bash
#
# fmt <string> <direction> <fillchar> <size>
# Formats a string by padding it to a specific size.
# <string> is the string you want formatted.
# <direction> is where you want the padding (l/L is left,
#    r/R and everything else is right).
# <fillchar> is the character or string to fill with.
# <size> is the desired size.
#
fmt()
{
    string="$1"
    direction=$2
    fillchar="$3"
    size=$4
    if [[ "${direction}" == "l" || "${direction}" == "L" ]] ; then
        while [[ ${#string} -lt ${size} ]] ; do
            string="${fillchar}${string}"
        done
        string="${string: -${size}}"
    else
        while [[ ${#string} -lt ${size} ]] ; do
            string="${string}${fillchar}"
        done
        string="${string:0:${size}}"
    fi
    echo "${string}"
}

 

# Unit test code.

echo "[$(fmt 'Hello there' r ' ' 20)]"
echo "[$(fmt 'Hello there' r ' ' 5)]"
echo "[$(fmt 'Hello there' l ' ' 20)]"
echo "[$(fmt 'Hello there' l ' ' 5)]"
echo "[$(fmt 'Hello there' r '_' 20)]"
echo "[$(fmt 'Hello there' r ' .' 20)]"
echo "[$(fmt 250 l 'x' 7)]"

This outputs:

[Hello there         ]
[Hello]
[         Hello there]
[there]
[Hello there_________]
[Hello there . . . . ]
[xxxx250]

and you're not limited to just printing them, you can also save the variables for later with a line such as:

formattedString="$(fmt 'Hello there' r ' ' 20)"