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Go to the previous, next
chapter.
This commands operate on individual characters.
Synopsis:
tr [option]... set1 [set2]
tr copies standard input to standard output, performing one of the
following operations:
- translate, and optionally squeeze repeated characters in the result,
- squeeze repeated characters,
- delete characters,
- delete characters, then squeeze repeated characters from the result.
The set1 and (if given) set2 arguments define ordered sets of
characters, referred to below as set1 and set2. These sets are the
characters of the input that tr operates on. The --complement (-c)
option replaces set1 with its complement (all of the characters that are not in
set1).
The format of the set1 and set2 arguments resembles the format of
regular expressions; however, they are not regular expressions, only lists of characters.
Most characters simply represent themselves in these strings, but the strings can contain
the shorthands listed below, for convenience. Some of them can be used only in set1
or set2, as noted below.
- Backslash escapes.
A backslash followed by a character not listed below causes
an error message.
- \a Control-G, \b Control-H, \f Control-L, \n Control-J, \r
Control-M, \t Control-I, \v Control-K, \ooo The character
with the value given by ooo, which is 1 to 3 octal digits, \\ A
backslash.
Ranges.
The notation m-n expands to all of the characters from m
through n, in ascending order. m should collate before n;
if it doesn't, an error results. As an example, 0-9 is the same as 0123456789.
Although GNU tr does not support the System V syntax that uses square
brackets to enclose ranges, translations specified in that format will still work as long
as the brackets in string1 correspond to identical brackets in string2.
Repeated characters.
The notation [c*n] in set2 expands to n
copies of character c. Thus, [y*6] is the same as yyyyyy.
The notation [c*] in string2 expands to as many copies
of c as are needed to make set2 as long as set1. If n
begins with 0, it is interpreted in octal, otherwise in decimal.
Character classes.
The notation [:class:] expands to all of the characters in the
(predefined) class class. The characters expand in no particular order, except
for the upper and lower classes, which expand in ascending
order. When the --delete (-d) and --squeeze-repeats
(-s) options are both given, any character class can be used in set2.
Otherwise, only the character classes lower and upper are
accepted in set2, and then only if the corresponding character class (upper
and lower, respectively) is specified in the same relative position in set1.
Doing this specifies case conversion. The class names are given below; an error results
when an invalid class name is given.
- alnum alnum Letters and digits. alpha alpha Letters. blank
blank Horizontal whitespace. cntrl cntrl Control characters. digit
digit Digits. graph graph Printable characters, not including space. lower
lower Lowercase letters. print print Printable characters, including
space. punct punct Punctuation characters. space space
Horizontal or vertical whitespace. upper upper Uppercase letters. xdigit
xdigit Hexadecimal digits.
Equivalence classes.
The syntax [=c=] expands to all of the characters that are
equivalent to c, in no particular order. Equivalence classes are a relatively
recent invention intended to support non-English alphabets. But there seems to be no
standard way to define them or determine their contents. Therefore, they are not fully
implemented in GNU tr; each character's equivalence class consists only of
that character, which is of no particular use.
tr performs translation when set1 and set2 are both
given and the --delete (-d) option is not given. tr
translates each character of its input that is in set1 to the corresponding
character in set2. Characters not in set1 are passed through
unchanged. When a character appears more than once in set1 and the
corresponding characters in set2 are not all the same, only the final one is
used. For example, these two commands are equivalent:
tr aaa xyz
tr a z
A common use of tr is to convert lowercase characters to uppercase. This
can be done in many ways. Here are three of them:
tr abcdefghijklmnopqrstuvwxyz ABCDEFGHIJKLMNOPQRSTUVWXYZ
tr a-z A-Z
tr '[:lower:]' '[:upper:]'
When tr is performing translation, set1 and set2
typically have the same length. If set1 is shorter than set2, the
extra characters at the end of set2 are ignored.
On the other hand, making set1 longer than set2 is not portable;
POSIX.2 says that the result is undefined. In this situation, BSD tr pads set2
to the length of set1 by repeating the last character of set2 as
many times as necessary. System V tr truncates set1 to the length
of set2.
By default, GNU tr handles this case like BSD tr. When the --truncate-set1
(-t) option is given, GNU tr handles this case like the System V
tr instead. This option is ignored for operations other than translation.
Acting like System V tr in this case breaks the relatively common BSD
idiom:
tr -cs A-Za-z0-9 '\012'
because it converts only zero bytes (the first element in the complement of set1),
rather than all non-alphanumerics, to newlines.
When given just the --delete (-d) option, tr
removes any input characters that are in set1.
When given just the --squeeze-repeats (-s) option, tr
replaces each input sequence of a repeated character that is in set1 with a
single occurrence of that character.
When given both --delete and --squeeze-repeats, tr
first performs any deletions using set1, then squeezes repeats from any
remaining characters using set2.
The --squeeze-repeats option may also be used when translating, in which
case tr first performs translation, then squeezes repeats from any remaining
characters using set2.
Here are some examples to illustrate various combinations of options:
Setting the environment variable POSIXLY_CORRECT turns off the following
warning and error messages, for strict compliance with POSIX.2. Otherwise, the following
diagnostics are issued:
-
- When the --delete option is given but --squeeze-repeats is
not, and set2 is given, GNU
tr by default prints a usage message
and exits, because set2 would not be used. The POSIX specification says that set2
must be ignored in this case. Silently ignoring arguments is a bad idea.
- When an ambiguous octal escape is given. For example, \400 is actually \40
followed by the digit 0, because the value 400 octal does not fit into a
single byte.
GNU tr does not provide complete BSD or System V compatibility. For
example, it is impossible to disable interpretation of the POSIX constructs [:alpha:],
[=c=], and [c*10]. Also, GNU tr does not delete
zero bytes automatically, unlike traditional Unix versions, which provide no way to
preserve zero bytes.
expand writes the contents of each given file, or standard
input if none are given or for a file of -, to standard output,
with tab characters converted to the appropriate number of spaces. Synopsis:
expand [option]... [file]...
By default, expand converts all tabs to spaces. It preserves backspace
characters in the output; they decrement the column count for tab calculations. The
default action is equivalent to -8 (set tabs every 8 columns).
The program accepts the following options. Also see section Common options.
- -tab1[,tab2]... -t tab1[,tab2]...
--tabs=tab1[,tab2]... -tab -t --tabs
If only one tab stop is given, set the tabs tab1 spaces apart (default is 8).
Otherwise, set the tabs at columns tab1, tab2, ... (numbered from
0), and replace any tabs beyond the last tabstop given with single spaces. If the tabstops
are specified with the -t or --tabs option, they can be
separated by blanks as well as by commas.
-i --initial -i --initial
Only convert initial tabs (those that precede all non-space or non-tab characters) on each
line to spaces.
unexpand writes the contents of each given file, or standard
input if none are given or for a file of -, to standard output,
with strings of two or more space or tab characters converted to as many tabs as possible
followed by as many spaces as are needed. Synopsis:
unexpand [option]... [file]...
By default, unexpand converts only initial spaces and tabs (those that
precede all non space or tab characters) on each line. It preserves backspace characters
in the output; they decrement the column count for tab calculations. By default, tabs are
set at every 8th column.
The program accepts the following options. Also see section Common options.
- -tab1[,tab2]... -t tab1[,tab2]...
--tabs=tab1[,tab2]... -tab -t --tabs
If only one tab stop is given, set the tabs tab1 spaces apart instead of the
default 8. Otherwise, set the tabs at columns tab1, tab2, ...
(numbered from 0), and leave spaces and tabs beyond the tabstops given unchanged. If the
tabstops are specified with the -t or --tabs option, they can be
separated by blanks as well as by commas. This option implies the -a option.
-a
--all -a --all Convert all strings of two or more spaces or tabs, not
just initial ones, to tabs.
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