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Manual Reference Pages  -  INDENT (1)


indent - indent and format C program source


     Comment indentation
     Preprocessor lines
     C syntax


indent [input-file [output-file]] [-bacc-| -nbacc ] [-bad-| -nbad ] [-bap-| -nbap ]
.Bk -words [-ei-| -ei ] [-eei-| -eei ] [-bbb-| -nbbb ]
.Ek [-bc-| -nbc ] [-bl] [-br] [-cn] [-cdn]
.Bk -words [-cdb-| -ncdb ]
.Ek [-ce-| -nce ] [-cin] [-clin] [-dn] [-din]
.Bk -words [-fbs-| -nfbs ] [-fc1-| -nfc1 ] [-fcb-| -nfcb ]
.Ek [-in] [-ip-| -nip ] [-ln] [-lcn] [-ldin] [-lp-| -nlp ] [-npro] [-pcs-| -npcs ] [-psl-| -npsl ] [-sc-| -nsc ]
.Bk -words [-sob-| -nsob ]
.Ek [-st] [-ta] [-troff] [-ut-| -nut ] [-v-| -nv ]


The indent utility is a C program formatter. It reformats the C program in the input-file according to the switches. The switches which can be specified are described below. They may appear before or after the file names.

NOTE: If you only specify an input-file, the formatting is done ‘in-place’, that is, the formatted file is written back into input-file and a backup copy of input-file is written in the current directory. If input-file is named '/blah/blah/file', the backup file is named 'file.BAK'.

If output-file is specified, indent checks to make sure that it is different from input-file.

The options listed below control the formatting style imposed by indent.
-bacc -, -nbacc
  If -bacc is specified, a blank line is forced around every conditional compilation block. For example, in front of every #ifdef and after every #endif. Other blank lines surrounding such blocks will be swallowed. Default: -nbacc .
-bad -, -nbad
  If -bad is specified, a blank line is forced after every block of declarations. Default: -nbad .
-bap -, -nbap
  If -bap is specified, a blank line is forced after every procedure body. Default: -nbap .
-bbb -, -nbbb
  If -bbb is specified, a blank line is forced before every block comment. Default: -nbbb .
-bc -, -nbc
  If -bc is specified, then a newline is forced after each comma in a declaration. -nbc turns off this option. Default: -nbc .
-br -, -bl
  Specifying -bl lines-up compound statements like this:
if (...)

Specifying -br (the default) makes them look like this:

if (...) {

-c n The column in which comments on code start. The default is 33.
-cd n The column in which comments on declarations start. The default is for these comments to start in the same column as those on code.
-cdb -, -ncdb
  Enables (disables) the placement of comment delimiters on blank lines. With this option enabled, comments look like this:
         * this is a comment

Rather than like this:

        /* this is a comment */

This only affects block comments, not comments to the right of code. The default is -cdb .

-ce -, -nce
  Enables (disables) forcing of ‘else’s to cuddle up to the immediately preceding ‘}’. The default is -ce .
-ci n Sets the continuation indent to be n. Continuation lines will be indented that far from the beginning of the first line of the statement. Parenthesized expressions have extra indentation added to indicate the nesting, unless -lp is in effect or the continuation indent is exactly half of the main indent. -ci defaults to the same value as -i .
-cli n Causes case labels to be indented n tab stops to the right of the containing switch statement. -cli0.5 causes case labels to be indented half a tab stop. The default is -cli0 .
-d n Controls the placement of comments which are not to the right of code. For example, -d1 means that such comments are placed one indentation level to the left of code. Specifying the default -d0 lines-up these comments with the code. See the section on comment indentation below.
-di n Specifies the indentation, in character positions, of global variable names and all struct/union member names relative to the beginning of their type declaration. The default is -di16 .
-dj -, -ndj
  -dj left justifies declarations. -ndj indents declarations the same as code. The default is -ndj .
-ei -, -nei
  Enables (disables) special else-if processing. If it is enabled, an if following an else will have the same indentation as the preceding if statement. The default is -ei .
-eei -, -neei
  Enables (disables) extra indentation on continuation lines of the expression part of if and while statements. These continuation lines will be indented one extra level. The default is -neei .
-fbs -, -nfbs
  Enables (disables) splitting the function declaration and opening brace across two lines. The default is -fbs .
-fc1 -, -nfc1
  Enables (disables) the formatting of comments that start in column 1. Often, comments whose leading ‘/’ is in column 1 have been carefully hand formatted by the programmer. In such cases, -nfc1 should be used. The default is -fc1 .
-fcb -, -nfcb
  Enables (disables) the formatting of block comments (ones that begin with ‘/*\n’). Often, block comments have been not so carefully hand formatted by the programmer, but reformatting that would just change the line breaks is not wanted. In such cases, -nfcb should be used. Block comments are then handled like box comments. The default is -fcb .
-i n The number of spaces for one indentation level. The default is 8.
-ip -, -nip
  Enables (disables) the indentation of parameter declarations from the left margin. The default is -ip .
-l n Maximum length of an output line. The default is 78.
-ldi n Specifies the indentation, in character positions, of local variable names relative to the beginning of their type declaration. The default is for local variable names to be indented by the same amount as global ones.
-lp -, -nlp
  Lines-up code surrounded by parenthesis in continuation lines. If a line has a left paren which is not closed on that line, then continuation lines will be lined up to start at the character position just after the left paren. For example, here is how a piece of continued code looks with -nlp in effect:
p1 = first_procedure(second_procedure(p2, p3),
  third_procedure(p4, p5));

With -lp in effect (the default) the code looks somewhat clearer:

p1 = first_procedure(second_procedure(p2, p3),
                     third_procedure(p4, p5));

Inserting two more newlines we get:

p1 = first_procedure(second_procedure(p2,

-npro Causes the profile files, './' and '~/', to be ignored.
-pcs -, -npcs
  If true (-pcs) all procedure calls will have a space inserted between the name and the ‘(’. The default is -npcs .
-psl -, -npsl
  If true (-psl) the names of procedures being defined are placed in column 1 - their types, if any, will be left on the previous lines. The default is -psl .
-sc -, -nsc
  Enables (disables) the placement of asterisks (‘*’s) at the left edge of all comments. The default is -sc .
-sob -, -nsob
  If -sob is specified, indent will swallow optional blank lines. You can use this to get rid of blank lines after declarations. Default: -nsob .
-st Causes indent to take its input from stdin and put its output to stdout.
-ta Automatically add all identifiers ending in "_t" to the list of type keywords.
-T typename
  Adds typename to the list of type keywords. Names accumulate: -T can be specified more than once. You need to specify all the typenames that appear in your program that are defined by typedef - nothing will be harmed if you miss a few, but the program will not be formatted as nicely as it should. This sounds like a painful thing to have to do, but it is really a symptom of a problem in C: typedef causes a syntactic change in the language and indent cannot find all instances of typedef.
  Causes indent to format the program for processing by troff(1). It will produce a fancy listing in much the same spirit as vgrind(1). If the output file is not specified, the default is standard output, rather than formatting in place.
-ut -, -nut
  Enables (disables) the use of tab characters in the output. Tabs are assumed to be aligned on columns divisible by 8. The default is -ut .
-v -, -nv
  -v turns on ‘verbose’ mode; -nv turns it off. When in verbose mode, indent reports when it splits one line of input into two or more lines of output, and gives some size statistics at completion. The default is -nv .

You may set up your own ‘profile’ of defaults to indent by creating a file called in your login directory and/or the current directory and including whatever switches you like. A ‘’ in the current directory takes precedence over the one in your login directory. If indent is run and a profile file exists, then it is read to set up the program’s defaults. Switches on the command line, though, always override profile switches. The switches should be separated by spaces, tabs or newlines.


'Box' comments. The indent utility assumes that any comment with a dash or star immediately after the start of comment (that is, ‘/*-’ or ‘/**’) is a comment surrounded by a box of stars. Each line of such a comment is left unchanged, except that its indentation may be adjusted to account for the change in indentation of the first line of the comment.

Straight text. All other comments are treated as straight text. The indent utility fits as many words (separated by blanks, tabs, or newlines) on a line as possible. Blank lines break paragraphs.

    Comment indentation

If a comment is on a line with code it is started in the ‘comment column’, which is set by the -c n command line parameter. Otherwise, the comment is started at n indentation levels less than where code is currently being placed, where n is specified by the -d n command line parameter. If the code on a line extends past the comment column, the comment starts further to the right, and the right margin may be automatically extended in extreme cases.

    Preprocessor lines

In general, indent leaves preprocessor lines alone. The only reformatting that it will do is to straighten up trailing comments. It leaves embedded comments alone. Conditional compilation (#ifdef...#endif) is recognized and indent attempts to correctly compensate for the syntactic peculiarities introduced.

    C syntax

The indent utility understands a substantial amount about the syntax of C, but it has a ‘forgiving’ parser. It attempts to cope with the usual sorts of incomplete and malformed syntax. In particular, the use of macros like:

    #define forever for(;;)

is handled properly.


The indent utility uses the HOME environment variable.


  profile file
  profile file


The indent command appeared in BSD 4.2 .


The indent utility has even more switches than ls(1).

A common mistake is to try to indent all the C programs in a directory by typing:

    indent *.c

This is probably a bug, not a feature.

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