A while ago I wrote this loop in a zsh script, and now I don't remember what it does, and I need to convert this script to run in sh.
for f in ${HOME}/.dotfiles/files/*(N) ${HOME}/.dotfiles/files/.*(N); do
symlink_prompt $(basename $f)
done
Can someone help me understand what this does, and how I can duplicate it in sh syntax?
The glob qualifier (N) causes the pattern to disappear entirely should it fail to match any files. There is no directly equivalent in POSIX shell; instead, you should simply check if f actually exists and continue if it does not. (If the pattern fails to match any files, f takes the literal pattern as its value instead.)
for f in "$HOME"/.dotfiles/files/* "$HOME"/.dotfiles/files/.*; do
[ -e "$f" ] || continue
symlink_prompt "$(basename "$f")"
done
If you are actually using bash, you can set the nullglob option instead.
shopt -s nullglob
for f in "$HOME"/.dotfiles/files/* "$HOME"/.dotfiles/files/.*; do
symlink_prompt "$(basename "$f")"
done
Related
What is the syntax to pass a variable to sed command that updates the second column in a CSV file. The variable name is $tag
This is the command I have used but I don't know where to put the variable exactly.
basename "$dec" | sed 's/.*/&,A/' >> home/kelsabry/Downloads/Tests/results.csv
where $decis variable that returns to me a certain directory.
Output:
Downloads, A
Documents, A
etc.
My command to pass the variable into sed to update the second column was:
basename "$dec" | sed 's/.*/&,'$tag'/' >> home/kelsabry/Downloads/Tests/results.csv
but it gave me this output:
Downloads, '$tag'
Documents, '$tag'
etc.
So, where should I write the variable $tag in sed command?
Unfortunately, sed is neither aware of fields nor capable of accepting variables. For that, you'd use shell or awk or shell or some other language.
sed is a Stream EDitor and in your example is taking input from stdin, not a variable.
If you do want to embed shell variables inside a sed script, understand that you are basically creating your sed script on-the-fly, and it's important to make sure you do it safely.
For example, if there's the possibility that your $tag variable might contain something that will cause misinterpretation of the sed script (i.e. perhaps it came from user input),
you need protection. In POSIX shell, perhaps something like this:
if [ "$tag" != "${tag#*[!A-Z]}" ]; then
printf 'ERROR: invalid tag\n' >&2
exit 1
fi
or even:
case "$tag" in
[A-Z]) : ;;
*) printf 'ERROR: invalid tag\n' >&2; exit 1 ;;
esac
then
# Note the alternative to `basename`
echo "${dec##*/}" | sed 's/$/,'"$tag"'/' >> path/to/file.csv
Note that sed doesn't know anything about fields or CSV. sed is simply being used to append a string on to the end of the line.
Of course, in csh (which perhaps shouldn't be used for scripted automation), you are missing the more useful parameter expansion tools, but you can still protect yourself in other ways:
if ( $%tag == 1 ) then
switch ($tag)
case [A-Z]:
printf '%s,%s\n' `basename "$dec"` "$tag"
breaksw
default:
printf 'ERROR: invalid tag\n'
exit 1
breaksw
endsw
else
printf 'ERROR: invalid tag\n'
exit 1
endif
(Note: this is untested. Mileage varies based on multiple conditions. May contain nuts.)
The issue you listed in your question was a quoting problem. You said: sed 's/.*/&,'$tag'/' >.
An alternative might be to use awk:
echo "${dec##*/}" | awk -v tag="$tag" '{print $0 OFS tag}' OFS=, >> path/to/file.csv
Awk is a more complete programming language, and supports named variables, unlike sed. The -v option allows you to pre-load an awk variable with the contents of a shell variable.
CSH is considered harmful by some. I'd recommend doing this in a POSIX shell instead, if only to take advantage of the much larger pool of experts who can help with your scripting questions. :)
I am trying to find executable files. Trying to use bourne shell /bin/sh for greater portability. Below script echos everything with find: at beginning of string.
#!/bin/sh
DIRS=`find / -perm -4000`
for DIR in "$DIRS"
do
case "$DIR" in
find:*);;
esac
done
QUESTION) Why is it echoing for find:*) when no commands are given?
If i add *) echo "$DIR";; clause to the case statement, it will echo the files that are executable for current user, this is all i really want, but isn't happening (i haven't scripted for /bin/sh really, but this has bewildered me)
Yeah sed, awk, cut can help immensely, but some of these commands most likely will not be available (why aren't they available. because they might not be!) so i thought a bourne shell version is more portable. Maybe there is a better way for /bin/sh substring matching, any ideas?
The lines that you are trying to get rid of presumably look like this:
find: `/root': Permission denied
That's an error message. The command substitution
`find ...`
only captures output, not errors. You need to add a redirection to include the errors:
`find ... 2>&1`
Also, -perm 4000 is the setuid bit, not an executable bit.
You can put find directly in the for loop
for DIR in `find / -perm -4000`
I just blindly followed a command from a tutorial to rename several folders at a time. Can anyone explain the meaning of "p;s" given as the argument to sed's -e option.
[root#LinuxD delsure]# ls
ar1 ar2 ar3 ar4 ar5 ar6 ar7
[root#LinuxD delsure]# find . -type d -name "ar*"|sed -e "p;s/ar/AR/g"|xargs -n2 mv
[root#LinuxD delsure]# ls
AR1 AR2 AR3 AR4 AR5 AR6 AR7
A sed script (the bit following the -e option) can contain multiple commands, separated by ;
The script in your example uses the p command to print the pattern space (i.e. the line just read from the input) followed by the s command to perform a substitution on the pattern space.
By default (unless the pattern space is cleared or the -n option is given to sed) after processing each line the current pattern spaceline is printed again, so the result of the substitution will be printed.
Another way to write the same thing would be:
sed -e "p" -e "s/ar/AR/g"
This separates the commands into two scripts. Another way would be:
sed "p;s/ar/AR/g"
because if the only argument to sed is a script then the -e option is not needed
The argument to the -e option is a script consisting of two commands. The first is p, which prints the unadulterated input, the second is a standard, global substitution. So for input ar1, this should output
ar1
AR1
The other part of this trick is the -n2 option on xargs, which forces it to only use two arguments at a time (instead of as many as it can handle, which would produce very different results).
One way in bash:
$ ls
ar6 ar7
$ find . -name 'ar*' | while IFS= read -r file; do echo mv "$file" "${file^^}"; done
mv ./ar6 ./AR6
mv ./ar7 ./AR7
get rid of the "echo" when you're happy with the output.
Can sh itself check if a program exists or is in path?
I.e., not with the help of the "which" program.
I don't believe sh can directly. But perhaps something like:
which() {
save_IFS=$IFS
IFS=:
for d in $PATH; do
test -x $d/$1 && echo $d/$1
done
IFS=$save_IFS
}
and here's a nice variation that uses a subshell so that restoring IFS is not necessary:
which() (
IFS=:
for d in $PATH; do
test -x $d/$1 && echo $d/$1
done
)
Also, (in bash) if the command has been executed in the past and bash has already done the PATH search, you can see what it found with hash -t.
bash-3.2$ hash -t which
bash: hash: which: not found
bash-3.2$ which foo
bash-3.2$ hash -t which
/usr/bin/which
The utility command -v $CMD is apparently a portable option (in the sense of being part of POSIX); see also the very similar (though bash-specific) question, in particular this answer.
Is there an idiomatic way to simulate Perl's diamond operator in bash? With the diamond operator,
script.sh | ...
reads stdin for its input and
script.sh file1 file2 | ...
reads file1 and file2 for its input.
One other constraint is that I want to use the stdin in script.sh for something else other than input to my own script. The below code does what I want for the file1 file2 ... case above, but not for data provided on stdin.
command - $# <<EOF
some_code_for_first_argument_of_command_here
EOF
I'd prefer a Bash solution but any Unix shell is OK.
Edit: for clarification, here is the content of script.sh:
#!/bin/bash
command - $# <<EOF
some_code_for_first_argument_of_command_here
EOF
I want this to work the way the diamond operator would work in Perl, but it only handles filenames-as-arguments right now.
Edit 2: I can't do anything that goes
cat XXX | command
because the stdin for command is not the user's data. The stdin for command is my data in the here-doc. I would like the user data to come in on the stdin of my script, but it can't be the stdin of the call to command inside my script.
Sure, this is totally doable:
#!/bin/bash
cat $# | some_command_goes_here
Users can then call your script with no arguments (or '-') to read from stdin, or multiple files, all of which will be read.
If you want to process the contents of those files (say, line-by-line), you could do something like this:
for line in $(cat $#); do
echo "I read: $line"
done
Edit: Changed $* to $# to handle spaces in filenames, thanks to a helpful comment.
Kind of cheezy, but how about
cat file1 file2 | script.sh
I am (like everyone else, it seems) a bit confused about exactly what the goal is here, so I'll give three possible answers that may cover what you actually want. First, the relatively simple goal of getting the script to read from either a list of files (supplied on the command line) or from its regular stdin:
if [ $# -gt 0 ]; then
exec < <(cat "$#")
fi
# From this point on, the script's stdin is redirected from the files
# (if any) supplied on the command line
Note: the double-quoted use of $# is the best way to avoid problems with funny characters (e.g. spaces) in filenames -- $* and unquoted $# both mess this up. The <() trick I'm using here is a bash-only feature; it fires off cat in the background to feed data from files supplied on the command line, and then we use exec to replace the script's stdin with the output from cat.
...but that doesn't seem to be what you actually want. What you seem to really want is to pass the supplied filenames or the script's stdin as arguments to a command inside the script. This requires sort of the opposite process: converting the script's stdin into a file (actually a named pipe) whose name can be passed to the command. Like this:
if [[ $# -gt 0 ]]; then
command "$#" <<EOF
here-doc goes here
EOF
else
command <(cat) <<EOF
here-doc goes here
EOF
fi
This uses <() to launder the script's stdin through cat to a named pipe, which is then passed to command as an argument. Meanwhile, command's stdin is taken from the here-doc.
Now, I think that's what you want to do, but it's not quite what you've asked for, which is to both redirect the script's stdin from the supplied files and pass stdin to the command inside the script. This can be done by combining the above techniques:
if [ $# -gt 0 ]; then
exec < <(cat "$#")
fi
command <(cat) <<EOF
here-doc goes here
EOF
...although I can't think why you'd actually want to do this.
The Perl diamond operator essentially loops across all the command line arguments, treating each as a filename. It opens each file and reads them line-by-line. Here's some bash code that will do approximately the same.
for f in "$#"
do
# Do something with $f, such as...
cat $f | command1 | command2
-or-
command1 < $f
-or-
# Read $f line-by-line
cat $f | while read line_from_f
do
# Do stuff with $line_from_f
done
done
You want to take the first argument and do something with it, and then either read from any files specified or stdin if no files?
Personally, I'd suggest using getopt to indicate arguments using the "-a value" syntax to help disambiguate, but that's just me. Here's how I'd do it in bash without getopts:
firstarg=${1?:usage: $0 arg [file1 .. fileN]}
shift
typeset -a files
if [[ ${##} -gt 0 ]]
then
files=( "$#" )
else
files=( "/dev/stdin" )
fi
for file in "${files[#]}"
do
whatever_you_want < "$file"
done
The ?: operator will die if there are no args specified, since you seem to want at least one arg either way. After grabbing that, shift the args over by one, and then either use the remaining args as your file list, or the bash special filehandle "/dev/stdin" if there were no other args.
I think that the "if no files are specified, use /dev/stdin - otherwise use the files on the command line" piece is probably what you're looking for, but the rest of the code is at least useful for context.
Also a little cheezy, but how about this:
if [[ $# -eq 0 ]]
then
# read from stdin
else
# read from $* (args)
fi
If you need to read and process line-by-line (which is likely) and don't want to copy/paste the same code twice (which is likely), define a function in your script and just pass the lines one-by-one to this function, and process them in said function.
Why not use ``cat #* in the script? For example:
x=`cat $*`
echo $x