Master Linux Text Manipulation with tr and fmt: Practical Examples

tr Command Overview

The tr utility reads from standard input, translates or deletes characters, and writes the result to standard output.

Syntax

tr [OPTION]... SET1 [SET2]

Character Set Notation

SET1 and SET2 may contain:

Literal characters (e.g., a, 5)

Ranges using a hyphen, e.g., a-z Octal escape sequences \NNN (1‑3 digits)

Common escape sequences: \n (newline), \t (tab), \r (carriage return), \b (backspace), \a (bell), \f (form feed), \v (vertical tab)

POSIX character classes inside [: :], e.g., [:lower:], [:upper:], [:digit:], [:space:], [:punct:], [:alnum:], [:blank:], [:cntrl:], [:graph:], [:print:], [:xdigit:] Repetition syntax for SET2: [CHAR*] repeats CHAR to match the length of SET1; [CHAR*REPEAT] repeats CHAR a specific number of times (REPEAT is octal).

Equivalence class [=CHAR=] matches all characters equivalent to CHAR.

Common Options

-d : delete characters in SET1.

-c : complement SET1 (operate on characters *not* in SET1).

-s : squeeze repeated characters in the output.

Typical Use Cases

Replace specific characters : cat file.txt | tr MTS5 ABCD Replaces M, T, S, 5 with A, B, C, D respectively.

Change case : cat file.txt | tr a-z A-Z or cat file.txt | tr [:lower:] [:upper:] Converts lower‑case to upper‑case. The reverse is achieved with tr A-Z a-z or tr [:upper:] [:lower:].

Replace spaces with tabs : cat file.txt | tr [:space:] '\t' Delete characters (using -d): cat file.txt | tr -d 'e' removes all e characters. cat file.txt | tr -d [:punct:] removes punctuation. cat file.txt | tr -d [:digit:] removes digits.

Keep only digits (complement) : cat file.txt | tr -cd [:digit:] outputs only the numeric characters.

fmt Command Overview

The fmt utility reformats plain‑text paragraphs to a specified line width, improving readability.

Syntax

fmt [-WIDTH] [OPTION] [FILE]

Key Options

-w N or -WIDTH N : wrap lines at N columns (default 75).

-s : split long lines only at whitespace, preventing word breaks.

-t : prepend a tab to the first line of each paragraph (indentation).

Example Workflow

Create a file file.txt with the following content:

Linux fan www.linuxmi.com shares open source news, tutorials on Linux, programming, big data, operations, and databases.
I was a big brother back then, the webmaster of Linux fanatics, and a Linux enthusiast using the desktop version. I write in my spare time and hope to share some useful tips with Linux beginners and enthusiasts.

Apply fmt with different options:

Default formatting (75 columns) : fmt file.txt Custom width (50 columns) : fmt -w 50 file.txt Split only at spaces : fmt -s file.txt Indent first line of each paragraph :

fmt -t file.txt

Sample Output

Using fmt -w 50 on the example text produces lines wrapped at 50 characters, preserving word boundaries. Using -s ensures no word is broken across lines, while -t adds a leading tab to each paragraph’s first line.

Practical Example Combining tr and fmt

Suppose linuxmi.txt contains: Linuxmi.com. Technology, Simplified! 56789 Typical processing steps:

Convert all lower‑case letters to upper‑case: cat linuxmi.txt | tr a-z A-Z Replace spaces with tabs: cat linuxmi.txt | tr [:space:] '\t' Delete punctuation and keep only alphanumeric characters: cat linuxmi.txt | tr -d [:punct:] | tr -d ' ' Reformat the cleaned text to a width of 40 columns: cat linuxmi.txt | tr -d [:punct:] | fmt -w 40 These pipelines illustrate how tr can be used for character‑level transformations (case conversion, deletion, substitution) and how fmt can subsequently format the resulting text into readable paragraphs.