Printf: Format and Print Data

The printf command is a powerful utility for formatting and printing data to standard output. It is commonly found as a shell built-in in shells like Bash, but a standalone GNU version also exists. This tool offers a more controlled and portable way to display information compared to the simpler echo command.

Shell Scripting with Printf

printf is invaluable in shell scripting for creating dynamic filenames, displaying user information, and generating formatted output. For instance, you can construct a timestamped filename for backups using printf -v FileName 'Backup_%(%F_%X)T.tgz' -1. This command assigns the formatted date and time to the FileName variable, making it suitable for archival purposes.

Basic Data Formatting with Printf

Displaying simple text with newlines is straightforward. The command printf '%s\n' "$USER" prints the current user's username followed by a newline character. This is a fundamental use case for ensuring clean and readable output in scripts.

Advanced Number Formatting

printf excels at formatting numbers. To output integers from 1 to one million with comma separators for readability, you can use printf "%'d\n" {1..1000000}. This feature significantly enhances the human readability of large numerical data. For zero-padding, ensuring a fixed width of 3 characters, use printf '%#.3d\n' 12. To space-pad a number to a width of 3 characters, use printf '%3d\n' 12. Left-aligning the number with space padding on the right is achieved by prefixing the width with a hyphen: printf '%-3d\n' 12.

Dynamic Field Spacing

When dealing with fields of varying lengths, printf allows for dynamic spacing. By using a variable for the field width, such as printf '%*s\n' $Integer 'Example Field', you can ensure consistent alignment and presentation of data, which is crucial for tabular output or structured logs.

# printf
# Format and print data

# This command is typically available as a built-in to many shells, such as the
# Bourne shell and the Bourne Again Shell. However, there also exists a GNU
# alternative, sometimes found over at `/usr/bin/printf`.

# Assign the current date (timestamp style) as a shell variable, using the Bash
# builtin, and make it a suitable filename for a Gzip-compressed Tar archive.
printf -v FileName 'Backup_%(%F_%X)T.tgz' -1

# Simple, feature-full, and portable way by which to echo(1) output to STDOUT.
# Here, the current user's username is displayed, followed by a new line.
printf '%s\n' "$USER"

# Using the Bash builtin, this will output one integer per line, from one to
# one million, in a human-readable kind of way, by appropriately
# comma-separating the units.
printf "%'d\n" {1..1000000}
# Getting these results by using the comma is actually also viable in AWK, but
# you'll likely have to jump through a quotation hoop to get access to it.

# Zero-pad a number in order to maintain a width of 3 characters. It's also
# possible to instead provide a `0` in-place of the hash (`#`).
printf '%#.3d\n' 12
# As above, but instead, space-pad the number. Prefix the `3` with a hyphen
# (`-`) to left-align the number, causing the padding to occur on the right.
printf '%3d\n' 12

# Set a field's spacing by using an integer provided as a variable. This is
# incredibly useful when you're dealing with inconsistent field lengths.
printf '%*s\n' $Integer 'Example Field'