mysql - How to detect whether the command output is being used in unix pipe -


in mysql -e option prints different formatting when used output pipe.

without pipe

[root@localhost commands]# $mysql_connect_str -e 'select 0/8' +--------+ | 0/8    | +--------+ | 0.0000 | +--------+

with pipe -- no formatting.

[root@localhost commands]# $mysql_connect_str -e 'select 0/8'| more 0/8 0.0000

how mysql command detecting output going fed command through pipe ?

there system call determine characteristics of file handle:

int fstat (int fd, struct stat *buf);         struct stat {            dev_t     st_dev;     /* id of device containing file */            ino_t     st_ino;     /* inode number */            mode_t    st_mode;    /* protection */            nlink_t   st_nlink;   /* number of hard links */            uid_t     st_uid;     /* user id of owner */            gid_t     st_gid;     /* group id of owner */            dev_t     st_rdev;    /* device id (if special file) */            off_t     st_size;    /* total size, in bytes */            blksize_t st_blksize; /* blocksize file system i/o */            blkcnt_t  st_blocks;  /* number of 512b blocks allocated */            time_t    st_atime;   /* time of last access */            time_t    st_mtime;   /* time of last modification */            time_t    st_ctime;   /* time of last status change */        };

by inspecting st_mode bits, program can determine type of device connected to. see man 2 fstat full details. in particular, there macros meant system independent distinguish between regular files, pipes, sockets, etc.

there system call determines whether file connection terminal:

int isatty(int fd);

description isatty() function tests whether fd open file descriptor referring terminal.

return value isatty() returns 1 if fd open file descriptor referring terminal; otherwise 0 returned, , errno set indicate error.


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