When a build goes wrong, the amount of error messaging can easily scroll off the screen. Usually the error is on the first line reported. Here’s a couple ways to make it easier to read just the lines you want.
The first is just to grep for the word ‘error.’ This works for gcc:
make 2>&1 | grep error |
Which produces
/root/devel/mctp_pcc/mctp_pcc.c:178:18: error: ‘name’ undeclared (first use in this function) /root/devel/mctp_pcc/mctp_pcc.c:178:52: error: ‘fe’ undeclared (first use in this function); did you mean ‘fd’? /root/devel/mctp_pcc/mctp_pcc.c:179:9: error: ‘ndev’ undeclared (first use in this function); did you mean ‘cdev’? /root/devel/mctp_pcc/mctp_pcc.c:179:37: error: ‘dev’ undeclared (first use in this function); did you mean ‘cdev’? /root/devel/mctp_pcc/mctp_pcc.c:182:17: error: ‘rc’ undeclared (first use in this function); did you mean ‘rq’? /root/devel/mctp_pcc/mctp_pcc.c:187:20: error: ‘idx’ undeclared (first use in this function); did you mean ‘ida’? /root/devel/mctp_pcc/mctp_pcc.c:190:24: error: ‘STATE_IDLE’ undeclared (first use in this function); did you mean ‘VTIME_IDLE’? /root/devel/mctp_pcc/mctp_pcc.c:193:34: error: ‘mctp_serial_tx_work’ undeclared (first use in this function) /root/devel/mctp_pcc/mctp_pcc.c:197:17: error: label ‘free_netdev’ used but not defined /root/devel/mctp_pcc/mctp_pcc.c:183:17: error: label ‘free_ida’ used but not defined /root/devel/mctp_pcc/mctp_pcc.c:199:1: error: no return statement in function returning non-void [-Werror=return-type] |
A bit of background…all Linux processes have 3 file descriptors (FD) by default. STDIN is for reading in information from other processes. STDIN is file descriptor 0. STDOUT is for, well, STANDARD’ output, or the output that the program is supposed to produce. STDOUT is FD 1. STDERR is for output that is not standard, and is intended for error messages. STDERR is FD 2.. Make and GCC spit their output into STDERR. The trick is to tell the program to redirect standard error into STDOUT via the magic symbol 2>&1. I read this in my head as “two goes into ampersand one.” STDERR is 2, STDOUT is 1.
If you want to get just the first set of line you can use the head command like this:
make 2>&1 | head -10 |
Which produces
make -C /lib/modules/6.2.0+/build M=/root/devel/mctp_pcc modules make[1]: Entering directory '/root/devel/linux' CC [M] /root/devel/mctp_pcc/mctp_pcc.o /root/devel/mctp_pcc/mctp_pcc.c: In function ‘create_mctp_pcc_nnetdev’: /root/devel/mctp_pcc/mctp_pcc.c:178:18: error: ‘name’ undeclared (first use in this function) 178 | snprintf(name, sizeof(name), "mctpipcc%x", fe); | ^~~~ /root/devel/mctp_pcc/mctp_pcc.c:178:18: note: each undeclared identifier is reported only once for each function it appears in /root/devel/mctp_pcc/mctp_pcc.c:178:52: error: ‘fe’ undeclared (first use in this function); did you mean ‘fd’? 178 | snprintf(name, sizeof(name), "mctpipcc%x", fe); |
This gets just the first 10 lines…use a different number if you want a different amount of output
These two options are fairly easy to type and thus don’t really call for scripting. As the amount of filtering gets longer,. you make want to make scripts that build up more complex selection of the output.
If you have control of your makefile, you can use the -Wfatal-errorsflag as is written up here, but I am calling into precanned Makefiles and it drops the flag. To modify Makefiles see this discussion.