linux - .sh script run by cronjob does not send email -

i have cronjob runs .sh script should make .txt file , send email.

i use sudo crontab -e

here script:

send_update.sh, -rwxrwxrwx

#!/bin/sh python /home/myusername/backend/mypy.py > update.txt sed -i '1s/^/subject: daily update /' update.txt sendmail myemail@gmail.com < /home/myusername/backend/update.txt echo "tester" >> tesert.txt 

interestingly, file run in echo print file not recieve email.

if run file command line typing sudo ./send_update.sh send email.

edit 1

the cron file line looks like:

* * * * * cd /home/myusername/backend && ./send_update.sh

edit 2

tesert.txt in same folder send_update.sh , printed cron job

edit 3

all files involved have permissions: -rwxrwxrwx

edit 4

#!/bin/sh python py2db.py > update.txt sed -i '1s/^/subject: daily update /' update.txt sed -i '$ d' update.txt date >> update.txt sendmail myemail@gmail.com < update.txt 

this new send_update.sh file. prints recent minute update.txt every minute, never sends email.

edit 5

as suggested changed file

#!/bin/sh python py2db.py > update.txt || echo "error python" >>/tmp/error.log sed -i '1s/^/subject: daily update /' update.txt || echo "error sed1" >>/tmp/error.log sed -i '$ d' update.txt || echo "error sed2" >>/tmp/error.log date >> update.txt || echo "error date" >>/tmp/error.log sendmail myemail@gmail.com < update.txt || echo "error sendmail" >>/tmp/error.log 

and after runs cat /tmp/error.log reads error sendmail

edit 6

after looking through logs have found:

sendmail: not found

i trying update path include sendmail. if can direct me on how appreciated.

edit 7

changing sendmail /usr/sbin/sendmail fixed issue , suggested error checking led me there.

add debug script , log errors in file, example :

#!/bin/sh python py2db.py > update.txt || echo "error python" >>/tmp/error.log sed -i '1s/^/subject: daily update /' update.txt || echo "error sed1" >>/tmp/error.log sed -i '$ d' update.txt || echo "error sed2" >>/tmp/error.log date >> update.txt || echo "error date" >>/tmp/error.log sendmail myemail@gmail.com < update.txt || echo "error sendmail" >>/tmp/error.log 

maybe don't have path 1 of command, try export path= too.