How to add characters to a string between specific characters in bash? - linux

Right now I'm working on creating a script in linux bash shell that adds the word "-BACKUP" to a file name between certain points. For example, if I had a file/string called file1.txt I would want to add the "-BACKUP" between "file1" and ".txt" to make "file1-BACKUP.txt". How would I go about doing that? Would I use the basename command anywhere? In this situation, the extension and stem could be anything, not just what I gave as an example. All help is appreciated!

Use the substring processing parameter expansion operator % to remove the suffix from the string, then append the new text. The variable must be enclosed in braces for substring processing parameter expansion to work.
var="file1.txt"
echo "${var%.txt}.BACKUP.txt"

Related

Bash: How to delete a multi-line string which may contain special characters from a string/file

I'm writing a script that at one point needs to remove a literal string (no regex matching needed) from a file. Both the string and file path are in script variables.
The problem is that the string is multi-line, and may also contain special characters. Additionally, not all lines in the string are unique in the file (but the string as a whole is), so I cannot go line by line to delete each individual one from the file.
For example, when I echo "$stringToDelete" from my script I get something like:
values(
/the/#quick/[]/"fox",
//jumped/over/the,
//lazy/{},
)
I've tried some approaches using sed and awk but any attempt fails with issues around either the newlines or the special characters. I've seen some answers invoking perl but couldn't get that to work.
Also I can easily read the full file's content into a variable, so the solution doesn't need to edit the file directly - a way to remove the stringToDelete from another string var is fine too.

How can I remove a newline (\n) at the end of a string?

The problem
I have multiple property lines in a single string separated by \n like this:
LINES2="Abc1.def=$SOME_VAR\nAbc2.def=SOMETHING_ELSE\n"$LINES
The LINES variable
might contain an undefined set of characters
may be empty. If it is empty, I want to avoid the trailing \n.
I am open for any command line utility (sed, tr, awk, ... you name it).
Tryings
I tried this to no avail
sed -z 's/\\n$//g' <<< $LINES2
I also had no luck with tr, since it does not accept regex.
Idea
There might be an approach to convert the \n to something else. But since $LINES can contain arbitrary characters, this might be dangerous.
Sources
I skim read through the following questions
How can I replace a newline (\n) using sed?
sed with literal string--not input file
Here's one solution:
LINES2="Abc1.def=$SOME_VAR"$'\n'"Abc2.def=SOMETHING_ELSE${LINES:+$'\n'$LINES}"
The syntax ${name:+value} means "insert value if the variable name exists and is not empty." So in this case, it inserts a newline followed by $LINES if $LINES is not empty, which seems to be precisely what you want.
I use $'\n' because "\n" is not a newline character. A more readable solution would be to define a shell variable whose value is a single newline.
It is not necessary to quote strings in shell assignment statements, since the right-hand side of an assignment does not undergo word-splitting nor glob expansion. Not quoting would make it easier to interpolate a $'\n'.
It is not usually advisable to use UPPER-CASE for shell variables because the shell and the OS use upper-case names for their own purposes. Your local variables should normally be lower case names.
So if I were not basing the answer on the command in the question, I would have written:
lines2=Abc1.def=$someVar$'\n'Abc2.def=SOMETHING_ELSE${lines:+$'\n'$lines}

Find space escape

Writing a small script in bash (MacOS in fact) and I want to use find, with multiple sources. Not normally a problem, but the list of source directories to search is held as a string in a variable. Again, not normally a problem, but some of them contain spaces in their name.
I can construct the full command string and if entered directly at the command prompt (copy and paste in fact) it works as required and expected. But when I try and run it within the script, it flunks out on the spaces in the name and I have been unable to get around this.
I cannot quote the entire source string as that is then just seen as one single item which of course does not exist. I escape each space with a backslash within the string held in the variable and it is simply lost. If I use double backslash, they both remain in place and again it fails. Any method of quoting I have tried is basically ignored, the quotes are seen as normal characters and splitting is done at each space.
I have so far only been able to use eval on the whole command string to get it to work but I felt there ought to be a better solution than this.
Ironically, if I use AppleScript I CAN create a suitable command string and run it perfectly with doShellScript (ok, that's using JXA, but it's the same with actual AppleScript). However, I have so far been unable to find the correct escape mechanism just in a bash script, without resorting to eval.
Anyone suggest a solution to this?
If possible, don't store all paths in one string. An array is safer and more convenient:
paths=("first path" "second path" "and so on")
find "${paths[#]}"
The find command will expand to
find "first path" "second path" "and so on"
If you have to use the string and don't want to use eval, split the string into an array:
string="first\ path second\ path and\ so\ on"
read -a paths <<< "$string"
find "${paths[#]}"
Paths inside string should use \ to escape spaces; wraping paths inside"" or '' will not work. eval might be the better option here.

How to rename a folder that contains smart quotes

I have a folder that was created automatically. The user unintentionally provided smart (curly) quotes as part of the name, and the process that sanitizes the inputs did not catch these. As a result, the folder name contains the smart quotes. For example:
this-is-my-folder’s-name-“Bob”
I'm now trying to rename/remove said folder on the command line, and none of the standard tricks for dealing with files/folders with special characters (enclosing in quotes, escaping the characters, trying to rename it by inode, etc.) are working. All result in:
mv: cannot move this-is-my-folder’s-name-“Bob” to this-is-my-folders-name-BOB: No such file or directory
Can anyone provide some advice as to how I can achieve this?
To get the name in a format you can copy-and-paste into your shell:
printf '%q\n' this*
...will print out the filename in a manner the shell will accept as valid input. This might look something like:
$'this-is-my-folder200\231s-name-200\234Bob200\235'
...which you can then use as an argument to mv:
mv $'this-is-my-folder200\231s-name-200\234Bob200\235' this-is-my-folders-name-BOB
Incidentally, if your operating system works the same way mine does (when running the test above), this would explain why using single-character globs such as ? for those characters didn't work: They're actually more than one byte long each!
You can use shell globbing token ? to match any single character, so matching the smart quotes using ? should do:
mv this-is-my-folder?s-name-?Bob? new_name
Here replacing the smart quotes with ? to match the file name.
There are several possibilities.
If an initial substring of the file name ending before the first quote is unique within the directory, then you can use filename completion to help you type an appropriate command. Type "mv" (without the quotes) and the unique initial substring, then press the TAB key to request filename completion. Bash will complete the filename with the correct characters, correctly escaped.
Use a graphical file browser. Then you can select the file to rename by clicking on it. (Details of how to proceed from there depend on the browser.) If you don't have a graphical terminal and can't get one, then you may be able to do the same with a text-mode browser such as Midnight Commander.
A simple glob built with the ? or * wildcard should be able to match the filename
Use a more complex glob to select the filename, and perhaps others with the same problem. Maybe something like *[^a-zA-Z0-9-]* would do. Use a pattern substitution to assign a new name. Something like this:
for f in *[^a-zA-Z0-9-]*; do
mv "$f" "${f//[^a-zA-Z0-9-]/}"
done
The substitution replaces all appearances of a characters that are not decimal digits, appercase or lowercase Latin letters, or hyphens with nothing (i.e. it strips them). Do take care before you use this, though, to make sure you're not going to make more changes than you intend to do.

Split a string in shell scripting explaination

I want to extract the directory. I have used the below mentioned shell script.
line='create word=/some/directory/name'
dir=${${${line##*=}#"'"}%"'"}
Though, it is working for me, I want to know the working of the 2nd line.
How exactly string split occur in the shell scripting.
These constructs are known as "Parameter Substitutions".
For example (directly from the Bash documentation):
${var##Pattern} Remove from $var the longest part of $Pattern that matches the front end of $var.
Parameter Substitutions in Bash
Parameter Substitutions in Zsh

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