在Linux系统中:
0 表示标准输入;
1表示标准输出;
2表示标准错误输出;
2>&1 表示将标准错误输出重定向到标准输入;
举一个例子:
a、不将标准错误输出 重定向到标准输入中。
[root@PC1 gffread-0.12.7.Linux_x86_64]# xxx ## 在终端随机输入一个命令,是一个错误输出 bash: xxx: command not found... [root@PC1 gffread-0.12.7.Linux_x86_64]# xxx | head -n 0 ## 结合管道,表明左侧的命令没有进入管道,也就是说标准错误输出直接输出到终端了。 bash: xxx: command not found...
b、将标准错误输出重定向到标准输入中。
[root@PC1 gffread-0.12.7.Linux_x86_64]# xxx bash: xxx: command not found... [root@PC1 gffread-0.12.7.Linux_x86_64]# xxx | head -n 0 bash: xxx: command not found... [root@PC1 gffread-0.12.7.Linux_x86_64]# xxx 2>& 1 | head -n 0 ## 将标准错误输出重定向到标准输入中
。
举例2:
a、
[root@PC1 gffread-0.12.7.Linux_x86_64]# ./gffread | head ## 管道不起作用 gffread v0.12.7. Usage: gffread [-g <genomic_seqs_fasta> | <dir>] [-s <seq_info.fsize>][-o <outfile>] [-t <trackname>] [-r [<strand>]<chr>:<start>-<end> [-R]][--jmatch <chr>:<start>-<end>] [--no-pseudo][-CTVNJMKQAFPGUBHZWTOLE] [-w <exons.fa>] [-x <cds.fa>] [-y <tr_cds.fa>][-j ][--ids <IDs.lst> | --nids <IDs.lst>] [--attrs <attr-list>] [-i <maxintron>][--stream] [--bed | --gtf | --tlf] [--table <attrlist>] [--sort-by <ref.lst>][<input_gff>]Filter, convert or cluster GFF/GTF/BED records, extract the sequence oftranscripts (exon or CDS) and more.By default (i.e. without -O) only transcripts are processed, discarding anyother non-transcript features. Default output is a simplified GFF3 with onlythe basic attributes.Options:--ids discard records/transcripts if their IDs are not listed in <IDs.lst>--nids discard records/transcripts if their IDs are listed in <IDs.lst>-i discard transcripts having an intron larger than <maxintron>-l discard transcripts shorter than <minlen> bases-r only show transcripts overlapping coordinate range <start>..<end>(on chromosome/contig <chr>, strand <strand> if provided)-R for -r option, discard all transcripts that are not fullycontained within the given range
b、管道生效
[root@PC1 gffread-0.12.7.Linux_x86_64]# ls gffread LICENSE README.md x [root@PC1 gffread-0.12.7.Linux_x86_64]# ./gffread 2>& 1 | head -n 5 ## 管道生效,仅仅输出5行 gffread v0.12.7. Usage: gffread [-g <genomic_seqs_fasta> | <dir>] [-s <seq_info.fsize>][-o <outfile>] [-t <trackname>] [-r [<strand>]<chr>:<start>-<end> [-R]][--jmatch <chr>:<start>-<end>] [--no-pseudo][-CTVNJMKQAFPGUBHZWTOLE] [-w <exons.fa>] [-x <cds.fa>] [-y <tr_cds.fa>]
。