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tr command

tr (translate) It can be used on the command line or Script One of the simplest case conversion commands on . For example, if you want a string to be all uppercase , You can do this with the command shown below ：

$ echo hello alvin | tr [:lower:] [:upper:]
HELLO ALVIN

The following is how the command is applied to Script Examples , write file depts The content of the plenary session is in capital form ：

$ echo "Enter department name: " | tr [:lower:] [:upper:] >> depts

The order of the above commands is changed to [:upper:] [:lower:] It's going to get the opposite result , All letters entered will be lowercase ：

$ echo "Enter department name: " | tr [:upper:] [:lower:] >> depts

You can use it. A-Z a-z Instead of [:upper:] [:lower:] To achieve the same effect ：

$ echo "Enter department name: " | tr a-z A-Z >> depts

awk command

awk Order to use toupper and tolower These two options complete the case conversion . The case conversion of the script described above can be done with this command in the following way ：

$ echo "Enter department name: " | awk '{print toupper($0)}' >> depts

The above is converted to capital letters , Here's how to convert to lower case letters ：

$ echo "Enter department name: " | awk '{print tolower($0)}' >> depts

sed command

sed （stream editor） The command can also do the case conversion well , The following command can also achieve the effect of the previous two commands ：

$ echo "Enter department name: " | sed 's/[a-z]/\U&/g' >> depts

To complete the reverse conversion , Just put the U Switch to L 、[a-z] Switch to [A-Z] that will do ：

$ echo "Enter department name: " | sed 's/[A-Z]/\L&/g' >> depts

Change the case of the text in the file
awk and sed Command can complete the case conversion of the entire document content , So if you need to convert the entire document to lowercase , You can use the following command to output the contents of a file in lowercase to the screen ：

$ awk '{print tolower($0)}' depts

The result is as follows ：

enter department name:
finance
billing
bookkeeping

Note that this result only converts what is printed on the screen to lowercase , There is no change in capital letters in the document itself , Use cat depts Command to see . If you want to really change the case of the document content , You can do this with the following command ：

$ awk '{print tolower($0)}' depts > depts-
$ mv depts- depts

sed Commands can be done and awk Same function , It's just a little different in usage , Its usage is as follows ：

$ sed 's/[A-Z]/\L&/g' depts

Just capitalize the first letter

Capitalize only the first letter of each word in a string , This can be done with the following command ：

$ echo design \& engineering| sed -e "s/\b\(.\)/\u\1/g"
Design & Engineering

The above command can only capitalize the first letter and keep the rest of the letters unchanged .

Make sure that only the initials are capitalized

When you need to do this with a lot of text , For example, to display the names of a large number of people in the correct format , What needs to be done will be a little harder . Here are two ways to do this ：

use sed Command complete

To make sure the results are correct , It needs to be more complicated sed Command format ：

$ echo design \& ENGINEERING | sed 's/\b\([[:alpha:]]\)\([[:alpha:]]*\)\b/\u\1\L\2/g'
Design & Engineering

use python Code completion

If your Linux Installed on python , You can use the following command to complete the capitalization of the text ,python The code is better than above sed The regular form of a command is much easier to understand ：

$ echo -n "design & engineering" | python3 -c "import sys; print(sys.stdin.read().title())"
Design & Engineering

Linux There are many commands for case conversion , Which one works better depends on whether you're dealing with a string of characters or an entire file . I hope the various commands in this article can help you , If you have any questions about these orders , Feel free to leave a comment ！Linux It's time to learn