I am writing a bash script to download files from ftp server using lftp. I wanted to delete the files based on the second input argument.
#!/bin/bash
cd $1
lftp -u found,e48RgK7s sftp://ftp.xxx.org << EOF
set xfer:clobber on
mget *.xml
if [ $2 = "prod"]; then
echo "Production mode. Deleting files"
mrm *.xml
else
echo "Non-prod mode. Keeping files"
fi
EOF
However, if statement is not allowed in the lftp block before EOF.
Unknown command `if'.
Unknown command `then'.
Usage: rm [-r] [-f] files...
Unknown command `else'.
How do I embed if statement in such block?
A command substitution will do:
#!/bin/bash
cd "$1" || exit
mode=$2
lftp -u found,e48RgK7s sftp://ftp.xxx.org << EOF
set xfer:clobber on
mget *.xml
$(
if [ "$mode" = "prod" ]; then
echo "Production mode. Deleting." >&2 # this is logging (because of >&2)
echo "mrm *.xml" # this is substituted into the heredoc
else
echo "Non-prod mode. Keeping files" >&2
fi
)
EOF
Note that inside the substitution for the heredoc, we're routing log messages to stderr, not stdout. This is essential, because everything on stdout becomes a command substituted into the heredoc sent to lftp.
Other caveats to command substitution also apply: They run in subshells, so a assignment made inside the command substitution will not apply outside of it, and there's a performance cost to starting them.
A more efficient approach is to store your conditional components in a variable, and expand it inside the heredoc:
case $mode in
prod)
echo "Production mode. Deleting files" >&2
post_get_command='mget *.xml'
;;
*)
echo "Non-production mode. Keeping files" >&2
post_get_command=
;;
esac
lftp ... <<EOF
set xfer:clobber on
mget *.xml
$post_get_command
EOF
Related
I'm trying to save the content of script into a file using command line, but I noticed that when the tee command detects linux commands such as $(/usr/bin/id -u), it execute the commands rather than saving the lines as it is. How to avoid the execution of the commands and saving the text exactly as I entered it?
$tee -a test.sh << EOF
if [[ $(/usr/bin/id -u) -ne 0 ]]; then
echo You are not running as the root user.
exit 1;
fi;
EOF
if [[ 502 -ne 0 ]]; then
echo You are not running as the root user.
exit 1;
fi;
Complete script contains many more lines, but I chose /usr/bin/id -u as a sample.
This has nothing to do with tee or appending to the file, it's how here-documents work. Normally variable expansion and command substitution is done in them.
Put single quotes around the EOF marker. This will treat the here-document like a single-quoted string, so that $ will not expand variables or execute command substitutions.
tee -a test.sh << 'EOF'
if [[ $(/usr/bin/id -u) -ne 0 ]]; then
echo You are not running as the root user.
exit 1;
fi;
EOF
if [[ $(/usr/bin/id -u) -ne 0 ]]; then
echo You are not running as the root user.
exit 1;
fi;
Running into a bit of an issue while trying to add a user prompt check to a existing script which was already working.
Here is the existing script, which is working...
#!/bin/sh
echo "**** Pulling changes into Production"
ssh user#example.com "$( cat <<'EOT'
cd example.com/html/ || exit
unset GIT_DIR
git pull
EOT
)"
Here is my modified script with a user prompt, which is broken.. and it is only broken when I add the ssh line. Works perfectly with just echoes.
#!/usr/bin/env bash
while true; do
read -p "Are you sure you want to pull changes into production? [y/N] " yn
case $yn in
[Yy]* )
ssh user#example.com "$( cat <<'EOT'
cd example.com/html/ || exit
unset GIT_DIR
git pull
EOT
)";
exit;;
[Nn]* )
echo "!!!! CANCELLING !!!!";
exit;;
* ) echo "Please answer yes or no.";;
esac
done
The error I'm getting is...
Syntax error: end of file unexpected (expecting ")")
EOT must appear at the beginning of the line. Your EOT appears somewhere in between, with lots of leading spaces.
Replace
EOT
By
EOT
How to write a bash shell script called 'abc' which takes one argument, the name of a directory, and adds the extension ".xyz" to all visible files in the directory that don't already have it
I have mostly written the code which changes the filenames inside the current directory but I can't get the script to accept an argument (directory name) and change the filenames of that directory
#!/bin/bash
case $# in
0) echo "No directory name provided" >&2 ; exit 1;;
1) cd "${1}" || exit $?;;
*) echo "Too many parameters provided" >&2 ; exit 1;;
esac
for filename in *
do
echo $filename | grep "\.xyz$"
if [ "$?" -ne "0" ]
then mv "$filename" "$filename.old"
fi
done
additional instructions include;
Within 'abc', use a "for" control structure to loop through all the non-hidden filenames
in the directory name in $1. Also, use command substitution
with "ls $1" instead of an ambiguous filename, or you'll descend into subdirectories.
EDIT: The top part of the question has been answered below, however the second part requires me to modify my own code according to the following instructions:
Modify the command substitution that's being used to create the loop values that will be placed into the "filename" variable. Instead of just an "ls $1", pipe the output into a "grep". The "grep" will search for all filenames that DO NOT end in ".xyz". This can easily be done with the "grep -v" option. With this approach, you can get rid of the "echo ... | grep ..." and the "if" control structure inside the loop, and simply do the rename.
How would I go about achieving this because according to my understanding, the answer below is already only searching through filenames without the .xyz extension however it is not being accepted.
Your description is a little unclear in places, so I've gone with the most obvious:
#!/bin/bash
# validate input parameters
case $# in
0) echo "No directory name provided" >&2 ; exit 1;;
1) cd "${1}" || exit $?;;
*) echo "Too many parameters provided" >&2 ; exit 1;;
esac
shopt -s extglob # Enables extended globbing
# Search for files that do not end with .xyz and rename them (needs extended globbing for 'not match')
for filename in !(*.xyz)
do
test -f && mv "${filename}" "${filename}.xyz"
done
The answer to the second part is this:
#!/bin/bash
for file in $(ls -1 "$1" | grep -v '\.old$'); do
mv "$file" "$file.old"
done
I got it from somewhere
when I read the book linux shell scripting cookbook
they say when you wanna print !,you shouldn't put it in double quote，or you can add \ before ! to escape it.
e.g.
$echo "Hello,world!"
bash: !:event not found error
$echo "Hello,world\\!"
Hello,world!
but in my situation(ubuntu14.04), I get the answer like that:
$echo "Hello,world!"
Hello,world!
$echo "Hello,world\\!"
Hello,world\!
So, why in my machine can't get the same answer?
Why the escape symbol \ was printed as a normal symbol?
When you're typing interactively to the shell, ! has special meaning, it's the history expansion character. To prevent this special meaning, you need to put it in single quotes or escape it.
echo 'Hello, world!'
echo "Hello, world\!'
The reason it's not happening on Ubuntu may be because it's running a newer version of bash, which is apparently more selective about when history expansion occurs. It seems to require ! to be followed by alphanumerics, not punctuation.
You don't need to do this in scripts, because history is not normally enabled there. It's just for interactive shells.
Create a shell script called file.sh:
#!/bin/bash
# file.sh: a sample shell script to demonstrate the concept of Bash shell functions
# define usage function
usage(){
echo "Usage: $0 filename"
exit 1
}
# define is_file_exits function
# $f -> store argument passed to the script
is_file_exits(){
local f="$1"
[[ -f "$f" ]] && return 0 || return 1
}
# invoke usage
# call usage() function if filename not supplied
[[ $# -eq 0 ]] && usage
# Invoke is_file_exits
if ( is_file_exits "$1" )
then
echo "File found"
else
echo "File not found"
fi
Run it as follows:
chmod +x file.sh
./file.sh
./file.sh /etc/resolv.conf
I have a bash program that will write to an output file. This file may or may not exist, but the script must check permissions and fail early. I can't find an elegant way to make this happen. Here's what I have tried.
set +e
touch $file
set -e
if [ $? -ne 0 ]; then exit;fi
I keep set -e on for this script so it fails if there is ever an error on any line. Is there an easier way to do the above script?
Why complicate things?
file=exists_and_writeable
if [ ! -e "$file" ] ; then
touch "$file"
fi
if [ ! -w "$file" ] ; then
echo cannot write to $file
exit 1
fi
Or, more concisely,
( [ -e "$file" ] || touch "$file" ) && [ ! -w "$file" ] && echo cannot write to $file && exit 1
Rather than check $? on a different line, check the return value immediately like this:
touch file || exit
As long as your umask doesn't restrict the write bit from being set, you can just rely on the return value of touch
You can use -w to check if a file is writable (search for it in the bash man page).
if [[ ! -w $file ]]; then exit; fi
Why must the script fail early? By separating the writable test and the file open() you introduce a race condition. Instead, why not try to open (truncate/append) the file for writing, and deal with the error if it occurs? Something like:
$ echo foo > output.txt
$ if [ $? -ne 0 ]; then die("Couldn't echo foo")
As others mention, the "noclobber" option might be useful if you want to avoid overwriting existing files.
Open the file for writing. In the shell, this is done with an output redirection. You can redirect the shell's standard output by putting the redirection on the exec built-in with no argument.
set -e
exec >shell.out # exit if shell.out can't be opened
echo "This will appear in shell.out"
Make sure you haven't set the noclobber option (which is useful interactively but often unusable in scripts). Use > if you want to truncate the file if it exists, and >> if you want to append instead.
If you only want to test permissions, you can run : >foo.out to create the file (or truncate it if it exists).
If you only want some commands to write to the file, open it on some other descriptor, then redirect as needed.
set -e
exec 3>foo.out
echo "This will appear on the standard output"
echo >&3 "This will appear in foo.out"
echo "This will appear both on standard output and in foo.out" | tee /dev/fd/3
(/dev/fd is not supported everywhere; it's available at least on Linux, *BSD, Solaris and Cygwin.)