I wrote a small script which:
prints the content of a file (generated by another application) on paper with a matrix printer
prints the same line into a backup file
removes the original file.
The script runs every minute by a cronjob and works fine as long as there are files to print. If there are no files to print, it prints an empty line on the matrix printer and in the backup file. I don't understand why this happens as i implemented an if statement which checks if there is a file to print before the print command is executed. This behaviour only happens if the script is executed by the cron and not if i execute it manually with ./script.sh. What's the reason of this? and how can i solve it?
Something i noticed on the side is that if I place an echo "hi" command in the script, its printed to the matrix printer and the backup file. I expected that its printed to the console console when it has no >> something behind. How does this work?
The script:
#!/bin/bash
# Make sure the backup directory exists
if [ ! -d /home/user/backup_logprint ]
then
mkdir /home/user/backup_logprint
fi
# Print the records if there are any
date=`date +%Y-%m-%d`
filename='_logprint_backup'
printer_path="/dev/usb/lp0"
if [ `ls /tmp/ | grep logprint | wc -l` -gt 0 ]
then
for f in `ls /tmp | grep logprint`
do
echo `cat /tmp/$f` >> "/home/user/backup_logprint/$date$filename"
echo `cat /tmp/$f` >> $printer_path
rm "/tmp/$f"
done
fi
There's no need for ls or an if statement. Just use a proper glob in the for loop, and if no file match, the loop won't be entered.
#!/bin/bash
# Don't check first; just let mkdir decide if
# anything actually needs to be created.
d=/home/user/backup_logprint
mkdir -p "$d"
filename=$(date +"$d/%Y-%m-%d_logprint_backup")
printer_path="/dev/usb/lp0"
# Cause non-matching globs to expand to an empty
# sequence instead of being treated literally.
shopt -s nullglob
for f in /tmp/*logprint*; do
cat "$f" > "$printer_path" && mv "$f" "$d"
done
Related
I am trying to make a script what looks at a folder and will automatically encode files that go into that folder using hand brake. I want to do this doing monitoring the folder using inotify putting the new additions to the folder into a list then using a cron job to encode them overnight. However when using a while loop to loop over the list handbrake only encodes the first file exists then the scripts carrys on to after the loop without doing every file in the list. Here is the script that is calling handbrake:
#!/bin/bash
while IFS= read -r line
do
echo "$(basename "$line")"
HandBrakeCLI -Z "Very Fast 1080p30" -i "$line" -o "$line.m4v"
rm "$line"
done < list.txt
> list.txt
When testing the loop with a simple echo instead of the HandBrakeCLI it works fine and prints out every file so I have no idea what is wrong.
Here is the scripts that is monitoring the folder incase that is the problem:
#!/bin/bash
if ! [ -f list.txt ]
then
touch list.txt
fi
inotifywait -m -e create --format "%w%f" tv-shows | while read FILE
do
echo "$FILE" >> list.txt
done
Any help would be great, thanks
EDIT:
Just to be more specific, the script works fine for the first file in the list.txt, it encodes it no problem and removes the old version, but then it doesn't do any of the others in the list
Taken from here
To solve the problem simply
echo "" | HandBrakeCLI ......
or
HandBrakeCLI ...... < /dev/null
I am looking to create a bash script that keeps checking a file in directory and perform certain operation on it. I am using while loop, if file does not exists I want that while loop stays quite and keeps on checking condition. Here is what i created but it keeps throwing error that file not found, if file is not there.
while [ ! -f /home/master/applications/tmp/mydata.txt ]
do
cat mydata.txt;
rm mydata.txt;
sleep 1; done
There are two issue in your implementation:
You should use the same (absolute or relative) path in your while loop test statement [ ! -f $file ] and in your cat and rm commands.
The cat command is looking for the file in the current working directory (pwd) and your while statement might be looking somewhere else and hence, your implementation is buggy and won't work as expected if your pwd isn't /home/master/applications/tmp.
You need to move your cat command and rm command after the while block. It doesn't make sense to cat a file if a file doesn't exist. I think your misplaced those commands.
Try this:
file="/home/master/applications/tmp/mydata.txt"
while [ ! -f "$file" ]
do
sleep 1
done
cat $file
rm $file
EDIT
As per suggestion from #Ivan, you could use until instead of while as it suits more to your requirements.
file="/home/master/applications/tmp/mydata.txt"
until [ -f "$file" ]; do sleep 1; done
cat $file
rm $file
Making a different assumption than abhiarora, I'll guess maybe you meant for the file to reappear, and you want it shown each time.
file=/home/master/applications/tmp/mydata.txt
while :
do if [[ -f "$file" ]]
then echo "$(<"$file")"
rm "$file"
fi
sleep 1
done
This creates an infinite loop. If that's NOT what you wanted, use abhiarora's solution.
Usually we may redirect a command output to a file, as following:
cat a.txt >> output.txt
As I tried, if cat failed, the output.txt will still be created, which isn't my expected. I know I could test as this:
if [ "$?" -ne "0"]; then
rm output.txt
fi
But this may cause some issues overhead when there's already such output.txt prior to my cat execution.
So I also need store the output.txt state before cat, if there's already such output.txt before cat execution, I should not rm output.txt by mistake... but there may still be problem on race condition, what if any other process create this output.txt right before my cat very closely?
So is there any simple way that, if the command fails, the redirection output.txt will be removed, or even not created?
Fixed output file names are bad news; don't use them.
You should probably redesign the processing so that you have a date-stamped file name. Failing that, you should use the mktemp command to create a temporary file, have the command you want executed write to that, and when the command is successful, you can move the temporary to the 'final' output — and you can automatically clean up the temporary on failure.
outfile="./output-$(date +%Y-%m-%d.%H:%M:%S).txt"
tmpfile="$(mktemp ./gadget-maker.XXXXXXXX)"
trap "rm -f '$tmpfile'; exit 1" 0 1 2 3 13 15
if cat a.txt > "$tmpfile"
then mv "$tmpfile" "$outfile"
else rm "$tmpfile"
fi
trap 0
You can simplify the outfile to output.txt if you insist (but it isn't safe). You can use any prefix you like with the mktemp command. Note that by creating the temporary file in the current directory, where the final output file will be created too, you avoid cross-device file copying at the mv phase of operations — it is a link() and an unlink() system call (or maybe even a rename() system call if such a thing exists on your machine; it does on Mac OS X) only.
You can't tell that the command has failed until it terminates, and by then it might have produced some output.
Probably a more useful condition is to avoid creating the output file until the command actually produces some output, and not worry about its status code.
This comes close:
command | { IFS= read -rn1 -d '' a &&
{ printf %s "$a" >> output.txt
cat >> output.txt
}
}
However, if the first character output by command is a NUL byte, the NUL won't be written to the output file. Since the extension of the output file is .txt, that's unlikely in this particular case, but it could be handled by adding the command
[[ -z $a ]] && printf '\0' >> output.txt
after the printf and before the cat.
I think this will work, check this out.
[ -e output.txt ] && (mv output.txt output.txt_bkp)
cat a.txt > /dev/null 2>&1;[ $? -eq 0 ] && (cat a.txt > output.txt)
another way as suggested by Jonathan,
[ -e output.txt ] && (mv output.txt output.txt_bkp)
if cat a.txt > /dev/null 2>&1
then
cat a.txt > output.txt
fi
*Note i edited this so my final functioning code is below
Ok so I'm writing a bash script to backup our mysql database to a directory, delete the oldest backup if 10 exist, and output the results of the backup to a log so I can further create alerts if it fails. Everything works great except the if loop to output the results, thanks again for the help guys code is below!
#! /bin/bash
#THis creates a variable with the date stamp to add to the filename
now=$(date +"%m_%d_%y")
#This moves the bash shell to the directory of the backups
cd /dbbkp/backups/
#Counts the number of files in the direstory with the *.sql extension and deletes the oldest once 10 is reached.
[[ $(ls -ltr *.sql | wc -l) -gt 10 ]] && rm $(ls -ltr *.sql | awk 'NR==1{print $NF}')
#Moves the bash shell to the mysql bin directory to run the backup script
cd /opt/GroupLink/everything_HelpDesk/mysql/bin/
#command to run and dump the mysql db to the directory
./mysqldump -u root -p dbname > /dbbkp/backups/ehdbkp_$now.sql --protocol=socket --socket=/tmp/GLmysql.sock --password=password
#Echo the results to the log file
#Change back to the directory you created the backup in
cd /dbbkp/backups/
#If loop to check if the backup is proper size and if it exists
if find ehdbkp_$now.sql -type f -size +51200c 2>/dev/null | grep -q .; then
echo "The backup has run successfully" >> /var/log/backups
else
echo "The backup was unsuccessful" >> /var/log/backups
fi
Alternatively, you could use stat instead of find.
if [ $(stat -c %s ehdbkp_$now 2>/dev/null || echo 0) -gt 51200 ]; then
echo "The backup has run successfully"
else
echo "The backup was unsuccessful"
fi >> /var/log/backups
Option -c %s tells stat to return the size of file in bytes. This will take care of both the presence of file and size greater than 51200. When the file is missing, stat will err out, thus we redirect error message to /dev/null. The logical or condition || will get executed only when the file is missing thus the comparison will make [ 0 -gt 100 ] false.
To check if the file exists and larger than 51200 bytes you could rewrite your if like this:
if find ehdbkp_$now -type f -size +51200c 2>/dev/null | grep -q .; then
echo "The backup has run successfully"
else
echo "The backup has was unsuccessful"
fi >> /var/log/backups
Other notes:
The find takes care two things at once: checks if file exists and size is greater than 51200.
We redirect stderr to /dev/null to hide the error message if the file doesn't exist.
If there was a file matching both conditions, then grep will match and exit with success, otherwise it will exit with failure
The final outcome of the grep is what decides the if condition
I moved the >> /var/log/backups after the closing fi, as it's equivalent this way and less duplication.
Btw if is NOT a loop, it's a conditional.
UPDATE
As #glennjackman pointed out, a better way to write the if, without grep:
if [[ $(find ehdbkp_$now -type f -size +51200c 2>/dev/null) ]]; then
...
I am trying to do an if/then statement, where if there is non-empty output from a ls | grep something command then I want to execute some statements. I am do not know the syntax I should be using. I have tried several variations of this:
if [[ `ls | grep log ` ]]; then echo "there are files of type log";
Well, that's close, but you need to finish the if with fi.
Also, if just runs a command and executes the conditional code if the command succeeds (exits with status code 0), which grep does only if it finds at least one match. So you don't need to check the output:
if ls | grep -q log; then echo "there are files of type log"; fi
If you're on a system with an older or non-GNU version of grep that doesn't support the -q ("quiet") option, you can achieve the same result by redirecting its output to /dev/null:
if ls | grep log >/dev/null; then echo "there are files of type log"; fi
But since ls also returns nonzero if it doesn't find a specified file, you can do the same thing without the grep at all, as in D.Shawley's answer:
if ls *log* >&/dev/null; then echo "there are files of type log"; fi
You also can do it using only the shell, without even ls, though it's a bit wordier:
for f in *log*; do
# even if there are no matching files, the body of this loop will run once
# with $f set to the literal string "*log*", so make sure there's really
# a file there:
if [ -e "$f" ]; then
echo "there are files of type log"
break
fi
done
As long as you're using bash specifically, you can set the nullglob option to simplify that somewhat:
shopt -s nullglob
for f in *log*; do
echo "There are files of type log"
break
done
Or without if; then; fi:
ls | grep -q log && echo 'there are files of type log'
Or even:
ls *log* &>/dev/null && echo 'there are files of type log'
The if built-in executes a shell command and selects the block based on the return value of the command. ls returns a distinct status code if it does not find the requested files so there is no need for the grep part. The [[ utility is actually a built-in command from bash, IIRC, that performs arithmetic operations. I could be wrong on that part since I rarely stray far from Bourne shell syntax.
Anyway, if you put all of this together, then you end up with the following command:
if ls *log* > /dev/null 2>&1
then
echo "there are files of type log"
fi