- Bash Quick Start Guide
- Tom Ryder
- 328字
- 2021-07-23 16:58:59
The printf command
The printf command works like echo, except the first argument you provide to it is a format string:
$ printf '%s\n' 'Hello!' Hello!
Notice that we had to put the format string in single quotes, to prevent the backslash from having special meaning to the shell. Notice also that we didn't have to use double quotes to get the newline from \n; the printf command did that for us.
You can use printf in much the same way you would use a printf() function in other languages, such as C. It supports most of the same format specifications as the printf(1) system command; you can type man 1 printf to see a list.
It's easier to print tricky strings with printf, where echo might struggle:
$ printf '%s\n' -n -n $ string=-n $ printf '%s\n' "$string" -n
You should always choose printf over echo in scripts, even though it's a little more typing.
printf also has a useful property where it will repeat the format string as necessary for each argument you provide it. This is a convenient way to print a list of arguments on individual lines:
$ printf '%s\n' foo bar baz foo bar baz
Note that we got three instances of the string-newline pattern from one format string.
Finally, Bash's printf has a %q pattern that can be used to quote special characters in a string with backslashes, so it can be reused safely in the shell. If you follow good quoting practices, you are unlikely to need this a lot in Bash, but it's useful to know it's there:
bash$ printf '%q\n' 'Watch out for thi$ $tring; it \has\ nasty character$!' Watch\ out\ for\ thi\$\ \$tring\;\ it\ \\has\\\ nasty\ character\$\!
- 協(xié)作機器人技術及應用
- Learning Apache Spark 2
- TestStand工業(yè)自動化測試管理(典藏版)
- Java開發(fā)技術全程指南
- Mastering D3.js
- JMAG電機電磁仿真分析與實例解析
- 傳感器技術應用
- Associations and Correlations
- Splunk Operational Intelligence Cookbook
- Linux服務與安全管理
- SAP Business Intelligence Quick Start Guide
- 深度學習與目標檢測
- 軟件構件技術
- Introduction to R for Business Intelligence
- 機床電氣控制與PLC