Command gofmt
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.