Overview
As its name suggests, `tr` (translate) translates or substitutes characters. For example, it specializes in simple character-level transformations such as changing lowercase to uppercase, replacing specific characters with others, or converting newline characters to spaces. Unlike `sed` or `awk`, which support complex pattern matching at the line level, `tr` is very fast and efficient for character-level processing.
Key Features
The main features of the `tr` command are as follows:
- Translates or deletes text character by character.
- Receives data only through standard input (stdin).
- Does not use regular expressions.
- Widely used with pipes (`|`) to process the output of other commands.
Basic `tr` Syntax
The `tr` command generally takes two character sets as arguments.
- `tr 'set1' 'set2'`: Translates characters in `set1` to characters in `set2` with a 1:1 correspondence.
- `tr -d 'set1'`: Deletes all characters present in `set1`.
Key Options
Frequently used `tr` command options are grouped by purpose.
1) Functional Options
2) Special Characters & Sets
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Usage Examples
Learn the functions of the `tr` command through various usage examples.
Convert Lowercase to Uppercase
echo 'hello world' | tr '[:lower:]' '[:upper:]'Converts lowercase letters received from standard input to uppercase and prints them.
Delete Specific Characters
echo 'hello world' | tr -d ' 'Deletes all spaces (` `) from the text.
Convert Newlines to Spaces
cat file.txt | tr '\n' ' 'Converts newline (`\n`) characters in file content to spaces (` `) and outputs it on a single line.
Squeeze Multiple Spaces
echo 'hello world' | tr -s ' 'Compresses sequences of repeated spaces into a single space. The `-s` option performs the function of squeezing repeated characters.
Convert Uppercase to Lowercase
echo 'HELLO WORLD' | tr 'A-Z' 'a-z'Converts uppercase letters received from standard input to lowercase and prints them.
Tips & Cautions
Here are some points to consider when using the `tr` command.
Tips
- `tr` does not directly accept filenames as arguments. You must pass text to standard input using commands like `cat` or `echo`.
- When passing strings as arguments, it is best to use single quotes (`'`) to prevent the shell from interpreting special characters.
- `tr` is simpler in functionality compared to `sed` or `awk`, but it has the advantage of being much faster for character-level transformation tasks.