forked from u-root/u-root
/
truncate.go
83 lines (70 loc) · 1.74 KB
/
truncate.go
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// Copyright 2013-2017 the u-root Authors. All rights reserved
// Use of this source code is governed by a BSD-style
// license that can be found in the LICENSE file.
// Truncate - shrink or extend the size of a file to the specified size
//
// Synopsis:
// truncate [OPTIONS] [FILE]...
//
// Options:
// -s: size in bytes
// -c: do not create any files
//
// Author:
// Roland Kammerer <dev.rck@gmail.com>
package main
import (
"flag"
"io/ioutil"
"log"
"os"
"github.com/rck/unit"
)
const cmd = "truncate [-c] -s size file..."
var (
create = flag.Bool("c", false, "Do not create files.")
size = unit.MustNewUnit(unit.DefaultUnits).MustNewValue(1, unit.None)
)
func init() {
flag.Var(size, "s", "Size in bytes, prefixes +/- are allowed")
defUsage := flag.Usage
flag.Usage = func() {
os.Args[0] = cmd
defUsage()
}
}
func usageAndExit() {
flag.Usage()
os.Exit(1)
}
func main() {
flag.Parse()
if !size.IsSet {
log.Println("truncate: ERROR: You need to specify -s <number>.")
usageAndExit()
}
if flag.NArg() == 0 {
log.Println("truncate: ERROR: You need to specify one or more files as argument.")
usageAndExit()
}
for _, fname := range flag.Args() {
st, err := os.Stat(fname)
if os.IsNotExist(err) && !*create {
if err = ioutil.WriteFile(fname, []byte{}, 0644); err != nil {
log.Fatalf("truncate: ERROR: %v\n", err)
}
if st, err = os.Stat(fname); err != nil {
log.Fatalf("truncate: ERROR: could not stat newly created file: %v\n", err)
}
}
final := size.Value // base case
if size.ExplicitSign != unit.None {
final += st.Size() // in case of '-', size.Value is already negative
}
if final < 0 {
final = 0
}
// intentionally ignore, like GNU truncate
os.Truncate(fname, final)
}
}