# tr — Translate, Delete and Squeeze Characters

> Practical guide to tr — translate, delete or squeeze characters from standard input. The filter for character-level transformations in shell pipelines.

Source: https://www.jpkc.com/db/en/cheatsheets/files-text/tr/

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tr (translate) is the filter for character-level transformations in the shell – it reads from standard input, replaces, deletes or squeezes individual characters, and writes the result to standard output. Unlike sed, tr works not with patterns but with character sets: you give it a source and a target set, and it maps them onto each other character by character. POSIX character classes such as `[:upper:]` or `[:digit:]` cover whole groups, and with `-d`, `-s` and `-c` you delete, condense or invert the selection. tr does not take filenames – it lives exclusively in the pipe.
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## Character Translation

`tr '<set1>' '<set2>'` — Replace characters in set1 with corresponding characters in set2.

```bash
echo 'hello' | tr 'aeiou' 'AEIOU'
```

`tr 'a-z' 'A-Z'` — Convert lowercase to uppercase.

```bash
echo 'hello world' | tr 'a-z' 'A-Z'
```

`tr 'A-Z' 'a-z'` — Convert uppercase to lowercase.

```bash
echo 'HELLO' | tr 'A-Z' 'a-z'
```

`tr '[:lower:]' '[:upper:]'` — Convert lowercase to uppercase using POSIX character classes.

```bash
cat file.txt | tr '[:lower:]' '[:upper:]'
```

`tr '<char>' '<char>'` — Replace a single character with another.

```bash
echo '2024/01/15' | tr '/' '-'
```

`tr ' ' '\n'` — Replace spaces with newlines (one word per line).

```bash
echo 'one two three' | tr ' ' '\n'
```

`tr '\n' ' '` — Replace newlines with spaces (join lines into one).

```bash
cat list.txt | tr '\n' ' '
```

`tr ',' '\t'` — Convert commas to tabs (CSV to TSV).

```bash
cat data.csv | tr ',' '\t' > data.tsv
```

`tr '\t' ','` — Convert tabs to commas (TSV to CSV).

```bash
cat data.tsv | tr '\t' ',' > data.csv
```

## Deleting Characters

`tr -d '<chars>'` — Delete all occurrences of the specified characters.

```bash
echo 'Hello, World!' | tr -d ',!'
```

`tr -d '[:digit:]'` — Remove all digits.

```bash
echo 'abc123def456' | tr -d '[:digit:]'
```

`tr -d '[:alpha:]'` — Remove all letters (keep digits, punctuation, etc.).

```bash
echo 'abc123def456' | tr -d '[:alpha:]'
```

`tr -d '[:space:]'` — Remove all whitespace (spaces, tabs, newlines).

```bash
echo '  hello   world  ' | tr -d '[:space:]'
```

`tr -d '\n'` — Remove all newlines (join all lines).

```bash
cat file.txt | tr -d '\n'
```

`tr -d '\r'` — Remove carriage returns (fix Windows line endings).

```bash
cat windows.txt | tr -d '\r' > unix.txt
```

`tr -d '[:punct:]'` — Remove all punctuation characters.

```bash
echo 'Hello, World! How are you?' | tr -d '[:punct:]'
```

## Squeezing Repeats

`tr -s '<chars>'` — Squeeze repeated characters into a single occurrence.

```bash
echo 'heeello' | tr -s 'e'
```

`tr -s ' '` — Collapse multiple spaces into a single space.

```bash
echo 'too    many    spaces' | tr -s ' '
```

`tr -s '\n'` — Remove blank lines (squeeze consecutive newlines).

```bash
cat file.txt | tr -s '\n'
```

`tr -s '[:blank:]'` — Squeeze all horizontal whitespace (spaces and tabs).

```bash
cat messy.txt | tr -s '[:blank:]'
```

`tr -s ' ' '\t'` — Squeeze multiple spaces and convert to a single tab.

```bash
ps aux | tr -s ' ' '\t'
```

## Complement

`tr -cd '<chars>'` — Delete all characters EXCEPT the specified ones.

```bash
echo 'abc123def456' | tr -cd '[:digit:]\n'
```

`tr -cd '[:alnum:]\n'` — Keep only alphanumeric characters and newlines.

```bash
echo 'Hello, World! #123' | tr -cd '[:alnum:]\n'
```

`tr -cd '[:print:]'` — Remove all non-printable characters.

```bash
cat binary-mixed.txt | tr -cd '[:print:]\n'
```

`tr -c '[:alnum:]' '_'` — Replace all non-alphanumeric characters with underscores.

```bash
echo 'Hello World! @2024' | tr -c '[:alnum:]\n' '_'
```

## Character Classes

`[:alpha:]` — All letters (a-z, A-Z).

```bash
tr -d '[:alpha:]'
```

`[:digit:]` — All digits (0-9).

```bash
tr -d '[:digit:]'
```

`[:alnum:]` — All letters and digits.

```bash
tr -cd '[:alnum:]'
```

`[:upper:] / [:lower:]` — Uppercase / lowercase letters.

```bash
tr '[:upper:]' '[:lower:]'
```

`[:space:]` — All whitespace (space, tab, newline, etc.).

```bash
tr -d '[:space:]'
```

`[:blank:]` — Horizontal whitespace only (space and tab).

```bash
tr -s '[:blank:]'
```

`[:punct:]` — All punctuation characters.

```bash
tr -d '[:punct:]'
```

`[:print:]` — All printable characters (including space).

```bash
tr -cd '[:print:]'
```

## Common Patterns

`tr -dc 'a-zA-Z0-9' < /dev/urandom | head -c <n>` — Generate a random alphanumeric string of n characters.

```bash
tr -dc 'a-zA-Z0-9' < /dev/urandom | head -c 32; echo
```

`echo '<text>' | tr '[:upper:]' '[:lower:]' | tr ' ' '-' | tr -cd '[:alnum:]-'` — Create a URL slug from text.

```bash
echo 'Hello World Blog Post' | tr '[:upper:]' '[:lower:]' | tr ' ' '-'
```

`cat <file> | tr -s ' ' '\n' | sort | uniq -c | sort -rn` — Word frequency count: split words, sort, count, sort by frequency.

```bash
cat article.txt | tr -s ' ' '\n' | sort | uniq -c | sort -rn | head -20
```

`echo '<ROT13>' | tr 'A-Za-z' 'N-ZA-Mn-za-m'` — ROT13 encode/decode a string.

```bash
echo 'Hello World' | tr 'A-Za-z' 'N-ZA-Mn-za-m'
```

`cat <file> | tr -cs '[:alpha:]' '\n'` — Extract words only (one per line), removing all non-alphabetic characters.

```bash
cat mixed.txt | tr -cs '[:alpha:]' '\n'
```

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## Conclusion

tr is small, fast and surprisingly versatile – ideal for tasks such as changing case, cleaning up Windows line endings (`tr -d '\r'`), condensing whitespace or splitting text into word lists. Keep its quirks in mind, though: tr always replaces character by character, never whole strings – for multi-character search-and-replace you need sed. The literal `\n` and `\t` must appear inside the respective argument and are interpreted by tr itself. tr only partially handles multibyte (UTF-8) characters, because it operates byte by byte; for umlauts and special characters it is therefore not always the right choice.

## Further Reading

- [GNU coreutils: tr](https://www.gnu.org/software/coreutils/manual/html_node/tr-invocation.html) – official reference with all options and character classes
- [tr(1) man page](https://man7.org/linux/man-pages/man1/tr.1.html) – the Linux manual page for tr
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## Related Commands

- [sed](https://www.jpkc.com/db/en/cheatsheets/files-text/sed/) – stream editor for pattern-based search and replace of whole strings
- [cut](https://www.jpkc.com/db/en/cheatsheets/files-text/cut/) – extract fields, characters or byte ranges from lines
- [paste](https://www.jpkc.com/db/en/cheatsheets/files-text/paste/) – merge lines of several files column by column