This question already has answers here:
echo "#!" fails -- "event not found"
(5 answers)
Closed 7 months ago.
echo "#!/bin/bash\nls -l /home/" > /home/myscript.sh
bash: !/bin/bash\nls: event not found
My script should be:
#!/bin/bash
ls -l /home/
Why does it ignore the echo "" string and think that there is some sort of event? Why does it not recognize #!/bin/bash as a special word?
the same thing happens when I
echo "#!/bin/bash" > /home/myscript.sh
so it's not the new line!
echo -e "#\!/bin/bash" > /home/myscript.sh
writes the file content as:
#\!/bin/bash
Why is this simple action going miserably wrong?
From the bash manpage:
Enclosing characters in double quotes preserves the literal value of
all characters within the quotes, with the exception of $, `, \,
and, when history expansion is
enabled, !.
So either use single quotes, or disable history expansion with set +o history.
But don't use echo. Instead, do :
printf '%s\n' '#!/bin/bash' 'ls -l /home/' > /home/myscript
or
cat > /home/myscript << 'EOF'
#!/bin/bash
ls -l /home/
EOF
echo -e '#!/bin/bash\nls -l /home/' > /home/myscript.sh
a combination of -e and using single quote fixed it.
Related
This question already has answers here:
Using variables inside a bash heredoc
(3 answers)
Trouble understanding the non-obvious use of backslash inside of backticks
(1 answer)
Closed 1 year ago.
I can't find out, how to mask the $ in the following shell statement. Any
help is appreciated!
#!/bin/bash
local result=`su -m user1 -c "sqlplus -s / as sysdba <<-EOF
SELECT cdb FROM v\$database;
exit
EOF"
`
You should single-quote EOF, e.g. <<-'EOF'
But then you also need to run the subprocess with $() instead of backquotes.
#!/bin/bash
local result=$(su -m user1 -c "sqlplus -s / as sysdba <<-'EOF'
SELECT cdb FROM v\$database;
exit
EOF")
BashFAQ/082 reports that “Backslashes (\) inside backticks are handled in a non-obvious manner”
$ echo "`echo \\a`" "$(echo \\a)"
a \a
$ echo "`echo \\\\a`" "$(echo \\\\a)"
\a \\a
# Note that this is true for *single quotes* too!
$ foo=`echo '\\'`; bar=$(echo '\\'); echo "foo is $foo, bar is $bar"
foo is \, bar is \\
So if you do not want to use $(...) you need 2 backslashes, i.e. \\$database and if you want to use neither $(...) nor single-quoted EOF, you need no less than 6 backslashes, i.e. \\\\\\$database
Do not use backticks. Use #(...).
local result=$(su -m user1 -c "sqlplus -s / as sysdba <<-EOF
SELECT cdb FROM v\\\$database;
exit
EOF
")
But anyway, if you do not want anything to expand, use single quotes.
local result=$(su -m user1 -c 'sqlplus -s / as sysdba <<-EOF
SELECT cdb FROM v\$database;
exit
EOF
')
And you could, redirect in the parent shell - it's going to be way simpler - and use a quoted stop word.
local result=$(su -m user1 -c 'sqlplus -s / as sysdba' <<-'EOF'
SELECT cdb FROM v$database;
exit
EOF
")
I'm getting this error
Syntax error: redirection unexpected
in the line:
if grep -q "^127.0.0." <<< "$RESULT"
How I can run this in Ubuntu?
<<< is a bash-specific redirection operator (so it's not specific to Ubuntu). The documentation refers to it as a "Here String", a variant of the "Here Document".
3.6.7 Here Strings
A variant of here documents, the format is:
<<< word
The word is expanded and supplied to the command on its
standard input.
A simple example:
$ cat <<< hello
hello
If you're getting an error, it's likely that you're executing the command using a shell other than bash. If you have #!/bin/sh at the top of your script, try changing it to #!/bin/bash.
If you try to use it with /bin/sh, it probably assumes the << refers to a "here document", and then sees an unexpected < after that, resulting in the "Syntax error: redirection unexpected" message that you're seeing.
zsh and ksh also support the <<< syntax.
if grep -q "^127.0.0." <<< "$RESULT"
then
echo IF-THEN
fi
is a Bash-specific thing. If you are using a different bourne-compatable shell, try:
if echo "$RESULT" | grep -q "^127.0.0."
then
echo IF-THEN
fi
It works for me on Ubuntu, if I complete you IF block:
if grep -q "^127.0.0." <<< "$RESULT"; then echo ""; fi
I’ve noticed that we can use curly braces to make some of the commands much shorter as it is evaluated into list of arguments.
Input:
echo a{,b,c}
Output:
a ab ac
How do I force the same behaviour when the arguments are passed from the file?
Input:
cat file.txt | xargs echo
Output:
a{,b,c}
Expected output - same as in the previous example.
That {} expansion is a bash / zsh feature, as such then you need to explicitly run it thru any of these shells, in your case would be (using -I<STRING> to let xargs replace it in the string before running it):
cat file.txt |xargs -I# bash -c 'echo #'
xargs calls the echo as found in the $PATH, not the shell's builtin echo.
check the list of bash expansions: brace expansion happens first, so it won't get a chance to expand in that pipeline.
You'll have to do something like
while read -r line; do eval echo "$line"; done < file.txt
which exposes you to all kinds of nasty attacks if someone puts something malicious in that file.
Other than asking why would you want to do this... I offer the following:
add the string to a file:
echo 'a{,b,c}' > /tmp/foo
put the string in a variable:
export thing=`cat /tmp/foo`
eval the string:
eval $thing
If you had a bunch of these in a file then run the file through a loop and eval the loop value:
echo 'a{,b,c}' >> /tmp/foo
echo 'a{,b,c}' >> /tmp/foo
echo 'a{,b,c}' >> /tmp/foo
for i in `cat /tmp/foo`; do eval echo $i; done
this question looks like Opening multiple tabs in gnome terminal with complex commands from a cycle, but I am looking for a more generic solution.
I have a C program that calls a script "xvi" with arguments. Each argument is originally enclosed within quotes (''') and each quote in an argument is isolated and back-slashed (this format is a prerequisite) ex:
xvi 'a file' 'let'\''s try another'
The script xvi must launch gnome-terminal with "-e vim args"
With xterm instead of gnome-terminal, this is easy because xterm assumes that "-e" is the last argument and passes all the tail to the shell, so the following is OK:
exec /usr/bin/xterm -e /usr/bin/vim "$#"
For gnome-terminal, "-e" is an option among others and we need to 'package' the whole command line in one argument. This is what I have done, which is OK: Enclose each argument within double quotes(\"arg\") and backslash any double quote within an argument:
cmd="/usr/bin/vim"
while [ "$1" != "" ] ; do
arg=`echo "$1" | sed -e 's/\"/\\\"/g'`
cmd="$cmd \"$arg\""
shift
done
exec gnome-terminal --zoom=0.9 --disable-factory -e "$cmd"
Again, this works fine and I am nearly happy with that.
Question: Is there any nicer solution, avoiding the loop?
Thanks
Untested, but you could probably finagle printf '%q' into doing the job:
exec gnome-terminal --zoom=0.9 --disable-factory -e "$(printf '%q ' "$#")"
I know this thread is old but recently I had a similar need and I created a bash script to launch multiple tabs and run different commands on each of them:
#!/bin/bash
# Array of commands to run in different tabs
commands=(
'tail -f /var/log/apache2/access.log'
'tail -f /var/log/apache2/error.log'
'tail -f /usr/local/var/postgres/server.log'
)
# Build final command with all the tabs to launch
set finalCommand=""
for (( i = 0; i < ${#commands[#]}; i++ )); do
export finalCommand+="--tab -e 'bash -c \"${commands[$i]}\"' "
done
# Run the final command
eval "gnome-terminal "$finalCommand
You just need to add your commands in the array and execute.
Gist link: https://gist.github.com/rollbackpt/b4e17e2f4c23471973e122a50d591602
I am trying to work out how to make bash (force?) expand variables in a string (which was loaded from a file).
I have a file called "something.txt" with the contents:
hello $FOO world
I then run
export FOO=42
echo $(cat something.txt)
this returns:
hello $FOO world
It didn't expand $FOO even though the variable was set. I can't eval or source the file - as it will try and execute it (it isn't executable as it is - I just want the string with the variables interpolated).
Any ideas?
I stumbled on what I think is THE answer to this question: the envsubst command:
echo "hello \$FOO world" > source.txt
export FOO=42
envsubst < source.txt
This outputs: hello 42 world
If you would like to continue work on the data in a file destination.txt, push this back to a file like this:
envsubst < source.txt > destination.txt
In case it's not already available in your distro, it's in the
GNU package gettext.
#Rockallite
I wrote a little wrapper script to take care of the '$' problem.
(BTW, there is a "feature" of envsubst, explained at
https://unix.stackexchange.com/a/294400/7088
for expanding only some of the variables in the input, but I
agree that escaping the exceptions is much more convenient.)
Here's my script:
#! /bin/bash
## -*-Shell-Script-*-
CmdName=${0##*/}
Usage="usage: $CmdName runs envsubst, but allows '\$' to keep variables from
being expanded.
With option -sl '\$' keeps the back-slash.
Default is to replace '\$' with '$'
"
if [[ $1 = -h ]] ;then echo -e >&2 "$Usage" ; exit 1 ;fi
if [[ $1 = -sl ]] ;then sl='\' ; shift ;fi
sed 's/\\\$/\${EnVsUbDolR}/g' | EnVsUbDolR=$sl\$ envsubst "$#"
Many of the answers using eval and echo kind of work, but break on various things, such as multiple lines, attempting to escaping shell meta-characters, escapes inside the template not intended to be expanded by bash, etc.
I had the same issue, and wrote this shell function, which as far as I can tell, handles everything correctly. This will still strip only trailing newlines from the template, because of bash's command substitution rules, but I've never found that to be an issue as long as everything else remains intact.
apply_shell_expansion() {
declare file="$1"
declare data=$(< "$file")
declare delimiter="__apply_shell_expansion_delimiter__"
declare command="cat <<$delimiter"$'\n'"$data"$'\n'"$delimiter"
eval "$command"
}
For example, you can use it like this with a parameters.cfg which is really a shell script that just sets variables, and a template.txt which is a template that uses those variables:
. parameters.cfg
printf "%s\n" "$(apply_shell_expansion template.txt)" > result.txt
In practice, I use this as a sort of lightweight template system.
you can try
echo $(eval echo $(cat something.txt))
You don't want to print each line, you want to evaluate it so that Bash can perform variable substitutions.
FOO=42
while read; do
eval echo "$REPLY"
done < something.txt
See help eval or the Bash manual for more information.
Another approach (which seems icky, but I am putting it here anyway):
Write the contents of something.txt to a temp file, with an echo statement wrapped around it:
something=$(cat something.txt)
echo "echo \"" > temp.out
echo "$something" >> temp.out
echo "\"" >> temp.out
then source it back in to a variable:
RESULT=$(source temp.out)
and the $RESULT will have it all expanded. But it seems so wrong !
Single line solution that doesn't need temporary file :
RESULT=$(source <(echo "echo \"$(cat something.txt)\""))
#or
RESULT=$(source <(echo "echo \"$(<something.txt)\""))
If you only want the variable references to be expanded (an objective that I had for myself) you could do the below.
contents="$(cat something.txt)"
echo $(eval echo \"$contents\")
(The escaped quotes around $contents is key here)
If something.txt has only one line, a bash method, (a shorter version of Michael Neale's "icky" answer),
using process & command substitution:
FOO=42 . <(echo -e echo $(<something.txt))
Output:
hello 42 world
Note that export isn't needed.
If something.txt has one or more lines, a GNU sed evaluate method:
FOO=42 sed 's/"/\\\"/g;s/.*/echo "&"/e' something.txt
Following solution:
allows replacing of variables which are defined
leaves unchanged variables placeholders which are not defined. This is especially useful during automated deployments.
supports replacement of variables in following formats:
${var_NAME}
$var_NAME
reports which variables are not defined in environment and returns error code for such cases
TARGET_FILE=someFile.txt;
ERR_CNT=0;
for VARNAME in $(grep -P -o -e '\$[\{]?(\w+)*[\}]?' ${TARGET_FILE} | sort -u); do
VAR_VALUE=${!VARNAME};
VARNAME2=$(echo $VARNAME| sed -e 's|^\${||g' -e 's|}$||g' -e 's|^\$||g' );
VAR_VALUE2=${!VARNAME2};
if [ "xxx" = "xxx$VAR_VALUE2" ]; then
echo "$VARNAME is undefined ";
ERR_CNT=$((ERR_CNT+1));
else
echo "replacing $VARNAME with $VAR_VALUE2" ;
sed -i "s|$VARNAME|$VAR_VALUE2|g" ${TARGET_FILE};
fi
done
if [ ${ERR_CNT} -gt 0 ]; then
echo "Found $ERR_CNT undefined environment variables";
exit 1
fi
foo=45
file=something.txt # in a file is written: Hello $foo world!
eval echo $(cat $file)
$ eval echo $(cat something.txt)
hello 42 world
$ bash --version
GNU bash, version 3.2.57(1)-release (x86_64-apple-darwin17)
Copyright (C) 2007 Free Software Foundation, Inc.
envsubst is a great solution (see LenW's answer) if the content you're substituting is of "reasonable" length.
In my case, I needed to substitute in a file's content to replace the variable name. envsubst requires that the content be exported as environment variables and bash has a problem when exporting environment variables that are more than a megabyte or so.
awk solution
Using cuonglm's solution from a different question:
needle="doc1_base64" # The "variable name" in the file. (A $ is not needed.)
needle_file="doc1_base64.txt" # Will be substituted for the needle
haystack=$requestfile1 # File containing the needle
out=$requestfile2
awk "BEGIN{getline l < \"${needle_file}\"}/${needle}/{gsub(\"${needle}\",l)}1" $haystack > $out
This solution works for even large files.
expenv () {
LF=$'\n'
echo "cat <<END_OF_TEXT${LF}$(< "$1")${LF}END_OF_TEXT" | bash
return $?
}
expenv "file name"
The following works: bash -c "echo \"$(cat something.txt)"\"