How to use strace to figure out what files are being accessed by a shell script

I had a situation where an ebs-supplied script adstrtal.sh would not start - it kept throwing error

ORA-12541: TNS:no listener

Although $TNS_ADMIN was correctly set, and sqlplus and tnsping would confirm that the database was open and the listener was up, accepting connections on the desired port.

The sqlnet.log file created in the same directory from which I executed adstrtal.sh displayed the connection being attempted:

Fatal NI connect error 12541, connecting to:
 (DESCRIPTION=(CONNECT_DATA=(SERVICE_NAME=EBS32.oric.no)(CID=(PROGRAM=sqlplus)(HOST=oric-ebsapp-utv.oric.no)(USER=ebs)))
 (ADDRESS=(PROTOCOL=TCP)(HOST=162.20.5.225)(PORT=1521)))

We are not using default port 1521, but a different port.

I then used strace to find the source of the error, like this:

strace -f -o /tmp/strace.out ./adstrtal.sh apps/****

When going through the /tmp/strace.out file, I was pointed in the right direction:

openat(AT_FDCWD, "$INST_TOP/ora/10.1.3/network/admin/EBS32_oric-ebsapp-utv_ifile.ora", O_RDONLY|O_LARGEFILE) = -1 ENOENT (No such file or directory)

Turns out that adstrtal.sh was looking for a tnsnames.ora entry not in the tnsnames.ora in $TNS_ADMIN ($INST_TOP/ora/10.1.2/network/admin) but rather in $INST_TOP/ora/10.1.3/network/admin.

As soon as I had added the correct tnsnames.ora entry, the adstrtall.sh script worked.