1 // Copyright 2009 The Go Authors. All rights reserved. 2 // Use of this source code is governed by a BSD-style 3 // license that can be found in the LICENSE file. 4 5 /* 6 Gofmt formats Go programs. 7 It uses tabs for indentation and blanks for alignment. 8 Alignment assumes that an editor is using a fixed-width font. 9 10 Without an explicit path, it processes the standard input. Given a file, 11 it operates on that file; given a directory, it operates on all .go files in 12 that directory, recursively. (Files starting with a period are ignored.) 13 By default, gofmt prints the reformatted sources to standard output. 14 15 Usage: 16 gofmt [flags] [path ...] 17 18 The flags are: 19 -d 20 Do not print reformatted sources to standard output. 21 If a file's formatting is different than gofmt's, print diffs 22 to standard output. 23 -e 24 Print all (including spurious) errors. 25 -l 26 Do not print reformatted sources to standard output. 27 If a file's formatting is different from gofmt's, print its name 28 to standard output. 29 -r rule 30 Apply the rewrite rule to the source before reformatting. 31 -s 32 Try to simplify code (after applying the rewrite rule, if any). 33 -w 34 Do not print reformatted sources to standard output. 35 If a file's formatting is different from gofmt's, overwrite it 36 with gofmt's version. If an error occurred during overwriting, 37 the original file is restored from an automatic backup. 38 39 Debugging support: 40 -cpuprofile filename 41 Write cpu profile to the specified file. 42 43 44 The rewrite rule specified with the -r flag must be a string of the form: 45 46 pattern -> replacement 47 48 Both pattern and replacement must be valid Go expressions. 49 In the pattern, single-character lowercase identifiers serve as 50 wildcards matching arbitrary sub-expressions; those expressions 51 will be substituted for the same identifiers in the replacement. 52 53 When gofmt reads from standard input, it accepts either a full Go program 54 or a program fragment. A program fragment must be a syntactically 55 valid declaration list, statement list, or expression. When formatting 56 such a fragment, gofmt preserves leading indentation as well as leading 57 and trailing spaces, so that individual sections of a Go program can be 58 formatted by piping them through gofmt. 59 60 Examples 61 62 To check files for unnecessary parentheses: 63 64 gofmt -r '(a) -> a' -l *.go 65 66 To remove the parentheses: 67 68 gofmt -r '(a) -> a' -w *.go 69 70 To convert the package tree from explicit slice upper bounds to implicit ones: 71 72 gofmt -r 'α[β:len(α)] -> α[β:]' -w $GOROOT/src 73 74 The simplify command 75 76 When invoked with -s gofmt will make the following source transformations where possible. 77 78 An array, slice, or map composite literal of the form: 79 []T{T{}, T{}} 80 will be simplified to: 81 []T{{}, {}} 82 83 A slice expression of the form: 84 s[a:len(s)] 85 will be simplified to: 86 s[a:] 87 88 A range of the form: 89 for x, _ = range v {...} 90 will be simplified to: 91 for x = range v {...} 92 93 A range of the form: 94 for _ = range v {...} 95 will be simplified to: 96 for range v {...} 97 98 This may result in changes that are incompatible with earlier versions of Go. 99 */ 100 package main 101 102 // BUG(rsc): The implementation of -r is a bit slow. 103 // BUG(gri): If -w fails, the restored original file may not have some of the 104 // original file attributes. 105