gofmt

Overview ¶

Gofmt formats Go programs. It uses tabs for indentation and blanks for alignment. Alignment assumes that an editor is using a fixed-width font.

Without an explicit path, it processes the standard input. Given a file, it operates on that file; given a directory, it operates on all .go files in that directory, recursively. (Files starting with a period are ignored.) By default, gofmt prints the reformatted sources to standard output.

Usage:

gofmt [flags] [path ...]

The flags are:

-d Do not print reformatted sources to standard output. If a file's formatting is different than gofmt's, print diffs to standard output. -e Print all (including spurious) errors. -l Do not print reformatted sources to standard output. If a file's formatting is different from gofmt's, print its name to standard output. -r rule Apply the rewrite rule to the source before reformatting. -s Try to simplify code (after applying the rewrite rule, if any). -w Do not print reformatted sources to standard output. If a file's formatting is different from gofmt's, overwrite it with gofmt's version. If an error occurred during overwriting, the original file is restored from an automatic backup.

Debugging support:

-cpuprofile filename Write cpu profile to the specified file.

The rewrite rule specified with the -r flag must be a string of the form:

pattern -> replacement

Both pattern and replacement must be valid Go expressions. In the pattern, single-character lowercase identifiers serve as wildcards matching arbitrary sub-expressions; those expressions will be substituted for the same identifiers in the replacement.

When gofmt reads from standard input, it accepts either a full Go program or a program fragment. A program fragment must be a syntactically valid declaration list, statement list, or expression. When formatting such a fragment, gofmt preserves leading indentation as well as leading and trailing spaces, so that individual sections of a Go program can be formatted by piping them through gofmt.

Examples ¶

To check files for unnecessary parentheses:

gofmt -r '(a) -> a' -l *.go

To remove the parentheses:

gofmt -r '(a) -> a' -w *.go

To convert the package tree from explicit slice upper bounds to implicit ones:

gofmt -r 'α[β:len(α)] -> α[β:]' -w $GOROOT/src

The simplify command ¶

When invoked with -s gofmt will make the following source transformations where possible.

An array, slice, or map composite literal of the form: []T{T{}, T{}} will be simplified to: []T{{}, {}} A slice expression of the form: s[a:len(s)] will be simplified to: s[a:] A range of the form: for x, _ = range v {...} will be simplified to: for x = range v {...} A range of the form: for _ = range v {...} will be simplified to: for range v {...}

This may result in changes that are incompatible with earlier versions of Go.

Notes ¶